There's been ZERO evidence to come forward of any wrong doing and all the 'evidence' the dems talk about that's "piling up" isn't even there. Now the dems have moved on to obstruction of justice, but what did Trump obstruct? Trump himself wasn't under investigation, so what actually did he obstruct? Trump could've plainly told Comey to stop the investigation and that would've been well within his rights to do so. He also has the right to pardon Flynn of any wrongdoing.
There are two real problems:
* There's evidence of Russian interference. Investigation of it will presumably involve looking at both campaigns. Since Trump benefited from it, and he and his stuff have more contact with Russians that is typical, it's reasonable that they would be looked at carefully.
* Several people associated with Trump seem to have been uncandid in responding to questions about their involvement with Russia.
It's not uncommon that what gets people in trouble is covering up activities, more than the activities themselves.
There are levels of investigation. What I described in the first bullet is consistent with a preliminary investigation. It doesn't mean there's any evidence that Trump did anything. I think we'd have heard if there were.
Personally I doubt that there was any actual collusion. It was obvious from the beginning that Trump tended to be positive towards Russia and their leaders, and Clinton tended to be more hawkish than usual. I don't think any collusion would be needed to convince Russia that they'd be better off with Trump as president.