Corker, Flake, Sasse, and Kasich

[Pericles]

https://www.publicpolicypolling.com/wp-content/uploads/2017/10/PPP_Release_National_103117.pdf

57% of Republicans want Trump, 36% want someone else. Trump vs Cruz is 57-27 , Trump vs Flake is 70-14, Trump vs Pence is 53-28, Trump vs Kasich is 66-24. Sadly they didn't poll Sasse or Corker, however it is clear that Kasich and Flake are bad candidates.

[Pericles]

I think Corker would be the strongest candidate, he's the only one who wasn't a NeverTrumper and has some credibility with the base. Plus, it's not impossible he could win or come close, in early 1975 Ford polled way ahead of Reagan but when the campaign got started the gap was closed. At least Corker would stand a slight chance, though would probably still lose.

[Pericles]

I think Corker would be the strongest candidate, he's the only one who wasn't a NeverTrumper and has some credibility with the base. Plus, it's not impossible he could win or come close, in early 1975 Ford polled way ahead of Reagan but when the campaign got started the gap was closed. At least Corker would stand a slight chance, though would probably still lose.

Corker lost any credibility he had with the "base" the second he defied Trump.

Probably but he'd still lose less badly than the other three and could consolidate many former Rubio and Cruz supporters. Trump wouldn't have been the nominee if it had been a two way race from the beginning. He would likely be the nominee in 2020 but it doesn't have to be 80-20, it can be 60-40 or 55-45.