US officials have evidence his campaign might have coordinated with the Russians to leak info damaging to Clinton. This explains why so many Democrats are certain he's getting impeached.
I don't have a link, it's on TV right now
Just like how Repubs thought Clinton was going to jail.
Essentially, someone has to produce the smoking gun.
I will say this, though: my interpretation is that if the smoking gun does come out that multiple people technically colluded with Russians in Trump's campaign (which will have to verified by the FBI/other groups and it looks like it is potentially being shown now), Trump will probably lash out in an unprecedented way. Try to take down Obama or Democrats maybe by declassifying things. Who knows.
If no smoking gun comes out, and nothing comes of this, then it could be disastrous for Democrats. Funnily enough, it's not necessarily democratic leaders who are leading the full charge as it is coming from the media and FBI, but the Dems will get blamed.
Overall, this whole thing is a mess. I'm not sure if I'm a big fan of the rabbit hole...but it seems someone/some group is going to take this huge L in full view of the public and international stage.