I think it's important to think about the context of support for Trump though. Are you asking "what would it take for a Trump supporter to change their vote in 2020?" or "what would it take for a Trump supporter to be in favor of impeachment (or similar)?"
If there were an election between DJT and HRC today I would not be surprised to see Trump win again. Do you really think a Republican is going to change their vote to Hillary? Maybe some independents, but with the electoral college, that may not matter.
However, if it's a situation where Trump gets impeached and Pence would become president, I think Republicans as a whole are more likely to support that because it guarantees that a member of their party will still be in office.