The reason? Republican Senator Romney will have what no other Republican Senator currently has, a Republican constituency that does not like President Trump. Trump came in third in the Republican primary in Utah in 2016 and in the general election a large number of voters voted for the independent and Mormon conservative Evan McMullin, rather than pull the lever for Trump or Hillary. For comparison, in 2016 Donald Trump won about 45 percent of the general election vote in Utah; in 2012, Romney won about 73 percent of the presidential vote there. Mormon voters, who make up the majority of voters in Utah, are perhaps the only conservative religious bloc in the country who are bothered by President Trump’s many infidelities and dubious business practices—Trump’s approval among Mormons trails behind white evangelicals by 14 points.
Thus, as Senator from Utah, Romney would have fewer electoral constraints on him to support the president than just about any other senator from a solidly red state. And he has already made it perfectly clear that he considers Trump a “con man,” an “imposter,” a “phony, a fraud.” He has criticized Trump for his business failures and for his sexual indiscretions. He will not commit to supporting him in 2020. On matters of Republican orthodoxy, like lowering taxes, Romney would vote like other Republicans, after all, Senators Jeff Flake (R-Ariz.) and Bob Corker (R-Tenn.)—also vocal Trump critics—voted for the tax bill. But it is the other votes Trump should fear, such as a vote to protect Bob Mueller’s job and keep the Russia investigation going.