Kevin Williamson thinks it’s “preposterous” to think that only Trump could have won in 2016. I’m a little more tolerant, though unconvinced, of that proposition. A couple of thoughts that bear on the question:
(1) Trump ran behind Republican candidates in a lot of swing states. Republican Senate candidates ran well ahead of him in Florida and Ohio, and slightly ahead of him in Wisconsin: point to Kevin. On the other hand, those Senate candidates were incumbents: half a point back.
(2) Other candidates would have had some vulnerabilities Trump didn’t. Rubio, for example, proposed to end federal taxes on capital income, favored a ban on abortion even in cases of rape and incest, and wanted to abolish the Department of Education. Each of those stands could have made for politically effective lines of attack by the Democrats.
(3) The other candidates might well have done better than Trump among white voters with college degrees, but would probably have also done worse among white voters without college degrees. Of course I’m piling speculation atop speculation here, but my guess is that nominating, say, Kasich would have led to a better popular-vote result for the Republicans but a narrower electoral victory.