It seems like every time the democrats try this, it backfires. The republicans, and especially Trump, are very effective at turning any political attacks back against the attackers. IMO, impeachment would be a dangerous tactic. Yes, it could work, but it could also backfire. If the democrats can nominate a reasonably moderate, intelligent, well spoken candidate, they should get rid of trump in the election. We have already had a long, drawn out investigation without solid proof of an impeachable offense, so just get on with the job of running the country. Propose some helpful programs like affordable college, rebuilding the infrastructure, a reasonable approach to climate change, and affordable health care, even though they will be shot down by the republicans. This could well be a more effective political tactic than continuing to attack Trump.
Edit: And even if by some miracle Trump was removed, what do we get? Mike Pence. That will solve all our problems.