Flake is setting himself up as the post-Trump rational Conservative.
He's going after the reasonable Republican vote. I doubt there's enough of them to do him any good.
Collins will be committing political suicide if she nixes K, but I suspect she might as well because the knuckle-draggers are probably going after her scalp anyway, no matter how she votes now.
As for Manchin...well, I don't exactly seem him as a Profile in Courage kind of guy.