As Speaker of the House, Paul Ryan is the leading Republican. Kelly Ayotte is running for re-election as the Republican Senator from New Hampshire, and representative of the many "down ticket" Republicans running for election in the year of the Trump. They represent the dilemma of Republican leaders. They can either denounce Trump or embrace him. If they embrace him they could lose enough independents that they lose the election. But if they criticize him, they could lose enough Trump supporters that they could lose the election. On the one hand they lose and on the other hand they .... lose.
(Kelly Ayotte has announced today that she won't be voting for Trump but will be writing in Pence, a clever way to distance herself from Trump without necessarily distancing herself from his supporters. This might work in her state.)
There is a fundamental problem with the Republican Party right now. There is not enough blanket to cover the wide distance of policy positions Republicans now cover.
On the one hand you have establishment Republicans who are essentially preparing for a 2020 election and are not about to be hurt long-term by an association with Trump now. Jeb Bush is the clearest example of this camp. This is honorable but it points to a problem: a lot of the folks excited about Trump won't vote for Jeb. Not in the recent primary and not in 2020. Trump or someone like him have that crowd. This rejection of Bush is historic. 1928 is the last time that the Republicans won the Oval Office without the name Richard Nixon or George Bush on the ticket as either president or vice president.
On the other hand you have the "basket of deplorables" who really do find Trump's refusal to pay taxes evidence that he's smart enough to beat the system, his crude statements about women proof that he's just a regular guy, his desire to ban Muslims evidence that he shares their instincts that Islam is terrorism, and his dismissal of the sacrifice of veterans a form of liberation from the tyranny of having to be "politically correct."
The Trump base is aware at a visceral level of a fact: we're living through a time of great change. What kind of change? When Obama took office, the US was 54% white Christian. When he leaves office, it'll be 47%. To the base who is afraid of trade and immigration, of various manifestations of the "other" that come in the form of liberals in big cities and refugees in small countries, this is further proof that a way of life - their way of life - is being driven to extinction.
As it turns out, the Republican Party's fragmentation has been evident before. In 1984, Reagan was re-elected with 58.8% of the popular vote. By 1992, George H. Bush lost re-election with only 37.4%. Within two elections, the Republicans lost a third of their national vote. In that same time, Democrats' share of the popular vote rose from 45.6% to 49.2% - a rise of just a few points. (Ross Perot grabbed a good share of the 1992 vote.) Democratic support is fairly stable as you can see below whereas Republican support swings wildly. Republicans have to get a candidate who appeals to religious conservatives who their fellow Republican working class voters think are prudes. Ted Cruz supporters might approach a political event as though it was church; Trump supporters as if it were a WWF match. If your candidate appeals to both groups - as Reagan did - you can't be beaten. If your candidate appeals to only one of the sub-groups (religious right or working class traditionalists), you can't win. (And this doesn't even mention the third group, the business conservatives more likely to donate than attend a rally. A Republican candidate also has to win over these business conservatives who want free trade and the working class who hate it.)
Simply put, the distance between the groups that comprise the Republican Party has become too great. You can no longer appeal to all of them with one politician. Those groups are so far apart that by the time you pull the policy and personality over from the one to cover the other, you've lost the first. Any Republican blanket is likely to be too small for today Republican party and it's not clear that they can find one politician who can create that coalition. It may no longer exist.