Trump is much stronger in debate than Democrats give him credit for. He basically won the nomination last time from showing up all the other Reps in debates.
The reality is, policy doesn't win debates. That lesson was learned back in 1960. Trump is tall and like or not, he has a very strong stage presence. Trump plays well in the TV sound bite era. If Democrats think they are going to win the general election debates on policy and Trump being shown to 'be stupid' they are going to get their asses kicked just lick 2016.
Bernie I think matches up best in a debate with Trump because he is a master of emotional appeals as well. But Biden and Warren I think Trump would defeat both in debate TBH
And Buttigieg has no chance. Too short.