While the Constitution clearly gives the Congress the responsibility to oversee the conduct of the President, the Republican House and Senate have not addressed the issue of potentially illegal payments received by Trump; reviewed Trump's mismanagement of foreign policy and executive agencies; and only reluctantly moved to have its intelligence committees investigate Russian interference and its ties to the Trump campaign. The reluctance of both the House and the Senate to exercise its constitutionally mandated oversight duties of Trump stands in stark contrast to its previous eagerness to oversee the Obama administration.
The GOP reluctance is all the more surprising because Trump is someone who many of the GOP do not consider a "true" Republican. As a businessman and during his campaign for President, not only did he fail to espouse many of the policies Republicans consider sacred, but he openly supported antithetical policies. And, although since winning office, he has pledged his support to the Republican agenda, one might reasonably suspect him to be viewed with enough suspicion to loosen the ties that would usually bind the Republican Congress to their party's president. Of course, one would only be surprised at the behavior of Republicans if one expected them to be principled.
"-There are three plausible reasons for the Republican dereliction of duty despite their tenuous loyalty to Trump: fear of reprisal by the Republican base; loss of someone who can, at least, partially heal the split between the GOP leadership and base; or support for his agenda and leadership style. Some pundits point to Trump's approval rating of over 80 percent among Republican voters as the key factor. They argue that this extraordinary approval rating coupled with gerrymandering within some states and the political culture of other states, such as those of the old confederacy, spell near certain defeat for any Republican candidate who appeared to criticize Trump. His overall approval ratings are somewhat down, hovering around the high 30s--something any Republican in a purple district or state will certainly consider. Nonetheless, there is evidence of continuing erosion among those Trump voters who were only weakly supportive of him. More importantly, in the short term, approval ratings this low make it virtually impossible for Trump to govern effectively. Still, these ratings do not portend a willingness to impeach him.
Another reason is that Trump may be a leader who can bind the party's various factions together. In much the same way Ronald Reagan was able to bind the far right fringe of the GOP to the mainstream, Donald Trump represents a lifeline to save the party from drifting back into weakly bound factions that are weakly bound and a chance to form the modern GOP. The primary commonality of these disparate factions was their distaste for the federal government. As a result the Party establishment has tried to use "lower taxes and less regulation" as a broad glue the factions together. But, as the base has less love for these policies, the GOP leadership has turned to seeking a plausible reincarnation of Ronald Reagan.
But, the primary appeal to all of these factions was resentment at the federal government for providing benefits to other "undeserving" groups. The introduction of the ACA, which helped older, rural, working-class whites, at the expense of the wealthy, intensified this resentment between GOP factions. The Party's espousal of emotion-laden social issues provided fig leaves to hide divisions within Party groups. Affordable health care, in a setting with increasing economic uncertainties, has highlighted the benefits families throughout the base are receiving from the once universally hated "Obama Care." As a result even the Republican Party is becoming more factionalized than it ever has been.
Of course, the GOP could have developed a policy agenda that would have been competitive in winning a majority of voters. For example, if the GOP could "hold its nose" and offer an agenda to provide working class voters with more of a social net, maybe, the Republican Party could be as competitive as it was during the Eisenhower years. But, instead it chose to support Donald Trump, a President who, by dint of his persona and brash salesmanship, has given the appearance of being on the side of the voters. Donald Trump, because he was not identified as a traditional Republican, was able to run on many policies that are counter to the typical Republican positions. Trump was able to promise that he would address issues that most concerned the Republican base. Notably, Trump promised to repeal the ACA and to replace it with better and more affordable health care; increase spending on the infrastructure and military, while he would reduce the debt, drain the swamp of privileged groups, and make America great again. And, more darkly, Trump promised his white supremacist followers that he would remove Latino immigrants and somehow whiten the complexion of the U.S.
Yet another possible reason that Congressional Republicans support and enable Trump is because his policies and authoritarian governing style actually represent the vision they desire for the U.S. Apart from Trump's apparent support for the GOP establishment's pronounced agenda of lower taxes and less regulation, which may be part of a transaction to forestall impeachment hearings, the GOP establishment may also support Trump's willingness to use undocumented immigrants while claiming to want strong borders, his full-throated support of voter suppression, and his readiness to throw over the base that supports him for the establishment that offered him lukewarm support during his campaign. The GOP base is also supporting Trump because of what he promises to deliver. That he has promised to deliver diametrically opposed benefits to the GOP establishment and base is a problem that even a grifting real estate developer may have difficulty fulfilling.
If Trump fails to pass the agenda that the GOP establishment wants, it is likely they will turn against him, perhaps in favor of Pence. As importantly regardless of whether the the agenda is passed, if the base sees unfilled promises, they will certainly turn against him. The difference is that failure to pass his agenda will occur relatively quickly. The base, on the other hand, is unlikely to realize that Trump has not kept his promises of industrial revitalization until at least the end of his first two years in office.
Even if it becomes clear that the Trump/GOP agenda cannot be passed in a Trump Presidency, Republicans are unlikely to remove him for a Pence Presidency. In the first place, Pence is not Trump--no one has ever suggested that Pence could shoot someone on Fifth Avenue and still retain even a modicum of support. Further, an impeachment and Senate trial will doom the chances of a Republican being elected in 2020. The only possibility that Republicans will impeach and convict Trump is if such damning evidence is uncovered against Trump, that they would be forced to remove him from office. What this means is that although a criminal offense is not a prerequisite to impeachment, Republicans would certainly require strong evidence of a serious crime. Anything less would be almost certainly be ignored.
GOP loyalty and allegiance to Trump are unlikely to wane in the near future. Even if Democrats take over the House in 2018, it is unlikely that Democrats will win enough Senate seats to convict and remove Trump. As a result, the only way Trump can be removed from office is if the Mueller investigation uncovers enough dirt on Trump to make Republicans impeach and convict him. Given the negative impact on the GOP if Trump is impeached and convicted, Republican Senators will certainly require a massive amount of evidence to convict him.
But, the importance of the Mueller investigation should not be underestimated. If properly used, the investigation and underlying Trump corruption can be used as an example of why Republicans should be defeated. And, "Republican loyalty" to Trump can be a key feature of the Democratic messaging and provide the motivation for Democrats and independents to vote against Republicans. In the meantime, this investigation will make it extremely difficult to pass Trump's legislative agenda--which I think is a very good thing.