Probably no one.
It will take 67 United States Senators (2/3rds of the Senate) to remove the soon-to-be-impeached Donald Trump from office in a Senate trial. There are currently 45 Democratic Senators and two independent Senators (who will vote with the Democrats). There are 53 Republican Senators.
In order to remove Trump from office, all of the Democrats and Independents will need to vote for removal and twenty Republicans will need to break with their party. I doubt this will happen. But it would certainly be revealing if a handful of principled Republicans (whether such Republicans exist is another question) broke with their party and voted to remove Trump from office.
Who might be the candidates for such a break with party? The best bets (granted, they are really long shots) are:
Mitt Romney (Utah): Strong critic of Trump with nothing to lose. Utah Republican’s don’t like Trump.
Susan Collins (Maine): She is not afraid to break with Trump, but did vote to confirm Bret Kavanaugh to the Supreme Court. Don’t hold your breath. If Collins votes for removal she might lose her seat in Maine.
Lisa Murkowski (Alaska): She has voted against Trump on healthcare and Kavanaugh.
Lamar Alexander (Tennessee): He is retiring and has been quiet. Maybe he will want to go out with integrity.
Of course Trump might turn this into a circus. If this happens, and witnesses are called, perhaps a few more minds might be changed or more information might be revealed. Mitch McConnell, of course, does not want this to happen.