Not all republicans are Trumpers. Some never have been.
Remember the Never-Trumpers during the Republican Primaries? They only made up 10-15% of the GOP, but they were there. Also remember that Trump won the nomination getting an average of 35% of the votes during the primaries. But in the large field, that was enough. Even on election day, 8 Nov 2016 only 47% of all republicans had a very favorable view of Trump, 28% somewhat favorable, 11% somewhat unfavorable and 15% very unfavorable. Question 11.
https://d25d2506sfb94s.cloudfront.net/cumulus_uploads/document/l37rosbwjp/econTabReport_lv.pdf
That at least a quarter of all Republicans who didn't care much for Trump. But since Trump received 88% of the Republican vote, even those who viewed Trump very unfavorably thought he was better than Hillary Clinton. Or at least half since Hillary did received 8% of the republican vote. 4% of the GOP vote went to third party candidates who probably thought both major party candidates sucked.
I would say there are quite a lot of Republicans not happy with Trump, but view him a lot better than the alternative.