For sake of brevity, I will not discuss each and every state and its polls except to note they generally undercount the poor, minorities and younger voters who are generally less likely to be polled or vote in off year elections. But, this year what is typical, may not be typical. While candidate preference is one thing, getting people to the voting booth is another, and as will be argued, in general, this race generates less passion for either party. Nor will I spend much time on the individual Senate races except to note trends that might influence the election. That task must be left to the experts will retroactively explain why the election turned out the way it did-as if they knew all along that the election of so and so was known and why it happened. .
Let us first note that only about six, perhaps eight, seats are really in play. Moreover and most commentators generally agree that Obama, has not simply lost his rock star status, but has become quite unpopular, even among some of his strongest early supporters. I am not basing my analysis on the polls most of which, at least in the tossup states, are fairly close. Thus while Nate Silver and perhaps Larry Sabato are among those thinking the Republicans are likely take the Senate, they offer caveats given the mood of the electorate and the disenchantment with both parties and little faith in the Senate. One of the main problems of prediction this year is the widespread feelings of helplessness and despair and pessimism that either party can do anything to assuage the despair. Obama and the Democrats are not very popular, but the Republicans fare even worse. Yet, like most elections, incumbents, typically with better name recognition and better funding are more likely to win, and this year that favors Republicans. But that said, a number of other factors qualify the typical trends.
Women voters: In general, women, especially single women voters, tend to be more liberal and women voters do constitute a slight majority of voters. Moreover, single women, eg the unmarried, divorced, and/or widowed, are indeed the largest single electoral bloc, and there are several reasons why we might fully expect women more likely to favor Democrats by perhaps 4% to 8% compared to men. It was clear in the last presidential election that women voters were instrumental in Obama's reelection. Why? As electoral studies have shown, women generally prefer policies that help the needy, benefit children, fund education, and support social benefits etc. rather than enhanced military spending or further advantage the already rich. Moreover, for many women healthcare, especially women's health issues are important issues. Moreover, a great many poor, single women have traditionally lacked health care insurance and despite the difficulties of getting ACA (Obamacare) up and running, for many women, having healthcare for themselves, their families and especially their children is a now benefit they do not want to give up. Contrary to the fears of Republicans, as Krugman has noted, the system has been working and today, approximately 8,000,000 people have healthcare insurance they mightn't have otherwise had. Moreover many who have already had health insurance, no longer fear being dropped in face of expensive care, or losing benefits for young adult children under 26 many of whom do not have healthcare. Further, the Republican "war on women" to sustain patriarchy has continued unabated, grows more angry, nasty, and venomous every day; most women not only know this, and generally know the Republicans have voted down Paycheck Fairness Act. For these reasons, there is anger toward the Republicans and fears of losing benefits, a majority of women are more likely to support Democrats. How this will play out is not certain, but with ACA now a fait accompli, conventional wisdom of the president party typically losing off year elections may not be the case this year.
Minorities: One of the major reasons prompting the resurgence of right populism, from the Tea Party to the move overtly nativist/racist groups has been the ressentiment toward the growing economic and cultural power of African-Americans which for the right wing has become closely intertwined with xenophobia toward other minorities that threaten the "superiority of their status, especially Spanish speakers. The various expressions of racism and ethnocentrism can be understood as attempt to preserve "heretofore privileged identities" and values traditional values based on the status advantages of being White, American, evangelical Protestant and religions that excludes indeed stigmatizes minorities, especially of color. The Tea Party needs to be understood as a protest against an Afro American president not a "true American," but one who would confiscate the wages of hard working Middle Americans and use those funds to support the lazy minorities who tend to be parasitic moochers, happy to live well without working for a living. Moreover, lazy Mexicans are not just taking American jobs (lazy but stealing jobs??) but if they enter the US, Obama insures they get food stamps, medical care and free housing for voting Democratic. While this kind of racist and/or xenophobic logic, indeed paranoid thinking has been part and parcel of the populist right in the USA for a long time, the growing political and cultural power African Americans, and influx of a variety of immigrants, has not only challenged the identities and the cultural hegemony of the populist right, but the changing demographics portend a multi-racial society. Furthermore, the limited, indeed lack of any recent progress over civil rights and/or the immigration bills, coupled with the blatant intolerance, and quite often actual violence toward minorities, think Arizona Sheriff Arpaio, think Treyvon Martin, think Ferguson, MO and Michael Brown, has fostered a great deal of anger and resentment toward Republicans that has will bolster African American and minority voter turnout and that turnout will favor Democrats. Further, it might be noted, there has been a steady migration of people from "blue states to red states" what has been called the purpling of America. While this may not include huge majorities, in a close race in conservative districts, a few percentage points of more liberal, cosmopolitan voters can swing a close race.
ACA (Obamacare): The Republican opposition to Obama care could be simply divided into two often overlapping reasons. Firstly, the business wing Republicans understand that providing a benefit clearly identified with the Democratic Party, and one that people will appreciate, will cost them votes. Secondly the populist right opposition most typically voiced by the Tea Party folks, offers a variety of less than coherent objections for example it would cover contraception which is of course anathema to evangelical Christians since it means that some people might have sex. Further, many equate any government provided benefit with socialism and it's pretty clear to them that one flu shot will turn anyone into a Maoist revolutionary. Finally, many believed that review boards would become death panels in which people 65 years or older are selected for euthanasia. In this 21st century version of Soylent Green, older folks might be recycled as big Macs. As previously noted, the positive impact of ACA, the general satisfaction and increasing acceptance has been duly noted by the Republicans who have greatly reduced the attacks as ACA is proving to be quite effective in reducing the numbers of the uninsured and improving health. The Republican strategists well understand the promises and threats to take away a benefit people receive may cost votes. Indeed, Democrats are now using it as a wedge issue, and with the waning of the influence of the Tea Party (see below), attacking ACA, that dog won't hunt. In fact, as I am suggesting, ACA will give the Democrats a few percentage points in races where it can matter.
I would like to go a bit further out on a limb and suggest that Mitch McConnell is in far less formidable shape than polls and pundits suggest (roughly a 10% lead). Yes, he is the incumbent, yes he is better funded, but 400,000 people in Kentucky now have health insurance that he first promised to eliminate. After Kentuckians were able to get health insurance, he said he would continue the programs for Kentucky but offered absolutely no indication of how can be funded without federal help. More recently he announced his willingness to again shut down the government that may well appeal to the tea party, but they are not the majority of the voters even in Kentucky. Allison Grimes has shown herself to be a very effective campaigner. When Elizabeth Warren came to Kentucky to campaign for her, massive crowds appeared. And the US, between the women's vote, minority votes and the numbers of people now getting healthcare, the assumption of McConnell's reelection may be a bit premature.
The Youth Vote: It is well know that older votes, especially retirees, are most likely to vote, especially in off year elections. Most pundits said that after OWS, the youth would give up on politics, but indeed, they did vote, in greater than expected rates and were a factor in the re-election. Moreover, while OWS has waned, the conditions that led to it, unemployed/underemployed youth, especially college graduates, faced with huge tuition debts, with almost 1/3 moving back home, are much less likely to sit out this election. With more time on their hands, and knowing that Elizabeth Warren has been working at lowering the costs of student loans, such youth are highly motivated to vote for Democrats. Furthermore, most millennials, being much more tolerant and liberal on social issues from approval of sex and drugs and rock 'n roll to rejecting racism, patriarchy, homophobia etc., the liberal tolerant millennial's are a growing force while the Tea Party is generally waning -- even if many of its candidates are well entrenched due to gerrymandering. The majority of millennials reject institutional religion even though they still believe in God. Similarly, a slight majority are willing to accept socialism, but most are not aware of what socialism is, other than free tuition healthcare. The result of the changing profile of youth, as already evident in 2012, suggests that many of these youth will be more likely to vote than is expected, and since most of the elections are likely to be close, the youth vote will favor Democrats.
The waning of the tea party: The history of right populism, surely since the days of the Know Nothing Party, shows that it tends to be cyclic, it arrives on the scene, full of sound and fury and then wanes, so too has its current instantiation, the Tea Party. Although right populism has a very long tradition, and today's movement conservatism, among the Tea Parties is rooted in that tradition, it is necessary to point out that it was the combination of the election of an African American at a time of a major economic crisis that made many sympathetic to its "small government" philosophy. Then came massive funding and organizational support from the Koch brothers and Dick Armey that made it seem as if a new, independent political force had arrived upon the scene, but indeed that "new" force was little more than traditional movement conservatism, typically Republican but rebranded with a new name. For a number of reasons its popularity, like most right wing, nativist movements has declined and its passions abated. One factor is that for many people in the Tea Party demographics, the economy is doing better, eg housing, automobile sales, credit card use etc. and as a result there is less hostility to the government. And Obama is on his way out so the intensity of their Tea Party passions have waned a bit. Another factor that might be noted is that the anti-immigration passions of 2010 have also cooled.  Parenthetically, it might be noted that the audience share of right wing shock jocks, especially Rush Limbaugh have been plummeting in both audience share and advertising revenues.
The mainstream Republicans have discovered that the 2010 Tea Party candidates often lose certain elections, especially when they campaign as not being a witch (Christine O'Donnell), or claim women's bodies shut down when "legitimately" raped (Clay Akin). So this year, the business wing of the Republican Party challenged the various movement conservatives and for the most part won, but the Eric Cantor defeat is instructive. Many Tea Partiers, see the mainstream candidates as not conservative enough. Many such "conservative" candidates "talk the talk" to get the values voters but they don't walk the walk and ultimately support the big business interests. Krugman, echoing what Thomas Frank said about Kansas, has suggested many right wing, movement conservatives have begun to notice the "bait and switch" tactics in which they are played for suckers and their agendas ignored and the promises made before their election are soon forgotten. They will be less than enthusiastic about voting for the business elites and their supporters-recall that one reason why Romney lost is that many right wing conservatives did not believe that Romney, having supporting gays, abortion, and state provided healthcare as governor was really "one of them". And indeed for many, seeing their extremist candidates lose primaries to the establishment, tempers their enthusiasm to vote for the more mainstream candidate they earlier opposed. And while the choir of pundits predict the Republicans are likely to win the Senate, none saw Cantor's defeat by an unknown econ prof as remotely possible. And by the way, this year, in the Kansas primaries, all the Koch Brothers money was not enough for the right wing conservatives to win. Combine that with the unpopularity of Gov. Brownback, perhaps nothing is the matter with Kansas anymore.
Moreover, as we have seen, the trends toward the legalization of pot, and growing acceptance of gay marriage, indicates that the cultural and voting power of the right wing has indeed waned. A central issue, at least for evangelical Christians, has been the preserving of the chastity of their young daughters. Despite all of the warnings of sin, despite the chastity balls, and promises of abstinence pledges to their fathers and to Jesus, there has been no evidence that these programs work. Indeed, young people from these evangelical backgrounds are more likely to get STDs-even while still "technically" virgins -- and once the threshold is been crossed are far more likely to wind up pregnant. The well-known stats of high teenage pregnancy in places like Texas, and far less often in Massachusetts says something.
While of course many of the tea partiers remain fervent in their homophobia, racism, patriarchy, and fundamentalist religion, their passions have dulled at the same time as more and more Americans have become more and more disenchanted with their extremist policies and the futility of their attempts to shut down Obama care and indeed, shut down the country or promise to reject refinancing the national debt. (Parenthetically it might be noted, that Obama has reduced the amount of national debt. reduced unemployment, and the markets are almost twice as high as when W left) Meanwhile, the threats to sue and/or impeach Obama have backfired
In sum, while the Tea Party remains a significant political force, especially in the South, their power to impose their agenda has not only fostered buyer's remorse, but a significant decline membership and fervor. Their extremist economic, political, cultural/religious values are more and more out of sync with the rest of the country. And much the same can be said about support for Republicans in general, more and more people seem them as supporting the rich while their own fortunes remain stagnant or in decline.
Import Export Bank: When people think of the Import Export Bank, few outside the policy wonk community know what that is. But in a couple of close races, it makes a considerable difference, especially in North Carolina and Louisiana where the Democrats (Hagan, Landrieu) basically support a bill favored by establishment Republicans who stand to benefit, but is opposed by movement Republicans. Surely, this is not a major issue for most voter, but will help at least two Democrats in tight races that if elected, may be the ones who keep the Senate in Democratic hands, and how ironic, thanks to support from some otherwise Republicans.