The most potent force standing in the way of a Democratic win in 2008 is the deteriorating unity in the Democratic Party. That could change but that is the biggest issue for Democrats right now. Whether or not the fractures in the party can be healed remains to be seen, but the person who is at fault for those fractures is Hillary Clinton.
Hillary is at fault for several reasons, but the biggest one is that it has been obvious since February 6th that she is not going to win the nomination. Most party leaders and pundits were predicting (correctly as we now know) that Obama would win the next eleven states in a row and this is the day after Obama had a massive victory in the February 5th Super Tuesday contests. Any other candidate would have quit at that point. It is the height of hubris and selfishness for Hillary to have continued. That she continued guaranteed that the race would degenerate into negativity and the politics of personal destruction.
If you are familiar with recreational athletics, you probably have heard of something called a "mercy rule". See http://www.momsteam.com/alpha/sports/basketball/basketball_mercy_rule.shtml and http://en.wikipedia.org/wiki/Mercy_rule . A mercy rule is a rule that says if you have a contest where the leader is ahead by a certain amount, the chance that the individual or team that is behind can reverse the situation is so improbable that it makes sense to stop the game and declare the individual or team that is ahead the victor. There are several important reasons beyond the probability of the reversal of fortunes to end a contest like that. If you read the first article I linked above it has a sentence that makes the point well:
"In addition, in many cases, the number and intensity of fouls increase, thereby putting player safety in jeopardy."
There is a tendency for people to get frustrated to the point where they act out in an ugly manner when they are losing. The several weeks of contests that Obama won in a row increased the frustration and anger level in the Clinton camp and that of her supporters to the point that all they want to do is "foul" Obama. From the perspective of the Obama camp and his supporters (as well as many neutral observers), in the last six weeks, Hillary and her campaign & supporters have thrown every nasty innuendo and accusation they could drum up at Obama. Hillary even went so far as to tout the attributes of the presumptive Republican nominee over Obama, a fellow Democrat. Disgust at the tactics of the Clinton campaign and her surrogates has inspired at least three articles of mine, http://www.opednews.com/articles/opedne_steven_l_080305_hillary_clinton___th.htm and http://www.opednews.com/articles/opedne_steven_l_080218_hillary_clinton___de.htm and http://www.opednews.com/articles/opedne_steven_l_080314_hillary_presses_obam.htm .
Although most people recognize that a lot of what is said in politics in general and campaigns in particular is rhetoric, particularly the attacks, there are a fair amount of people that believe them and form lasting opinions based on the things that are said. When the race for the nomination is all over, Hillary will endorse Obama and many of her campaign people will go to work for him. That is how little anyone should believe what is coming out of Hillary's camp right now. Unfortunately, the attacks being made by Hillary and her surrogates in addition to the overall tone with which she has conducted her campaign since February 6th will cause many of her current supporters to question whether they should support and vote for Obama in the general election. Hillary is going to have to work hard to convince them that they should support Obama and how she does that is going to be an interesting tightrope to walk considering that she could come across as a liar for some of the things she has said. If she fails to be able to do that, and it is no guarantee at this point that she reverse the damage to the mindset of some of her supporters enough so that she can bring them to support Barack once it is all over, not only will she have cost the Democrats the White House, she will have caused a number of down ticket Democrats in the US House and Senate and state legislatures and governors mansions to lose as well.
I think many prominent Democrats realize this is where we are and are upset at the situation and angry at Hillary. I think that is one of the reasons for some of the more pointed comments coming from Nancy Pelosi, for instance, on a unity ticket. I think she recognizes the danger to Democrats retaining the house and senate and is concerned. The longer Hillary waits to drop out and endorse Obama, the worse this is going to get and the higher the probability of a catastrophic outcome for Democrats on Election Day. Historians will no doubt make the same connections I have made and blame Hillary for the loss if that happens. Hillary's withdrawal from this race is six weeks overdue. It is time for her to regain her grip on reality, put her party and her country above herself and concede the race to Obama.