There has to be a reason for impeachment, but in the majority, Dems could do it anyway, and even if it happens, it takes 2/3 of the senate to convict. Unless Mueller has something criminal, Trump won't be convicted, even if impeached just because they have the numbers. If the Dems, however, after the election, had 2/3 of the senate, then they could convict him, but - for what? Still think it would have to be a criminal charge. Just because they don't like him, won't work.