~Six months from now, will there be any Democratic Senators calling on Trump to resign, and who will they be?
I think you left out the word "not" here.
I think people are getting ahead of themselves here. Right now, AFAIK, no prominent Democrats are calling on Trump to resign. They're calling for an investigation. "Investigation" can last for months/years, so it's not clear to me how far things will have actually advanced by the fall of this year.
I think if you put all the democratic senators into a hypnotic trance, and forced them to give an answer on whether they think Trump should resign, about a third would say yes.