Aside from the investigation being far from over and wanting the GOP to be the ones who first filed, the other reason I didn’t want to see impeachment brought up this early is I know that the GOP is going to now make this a campaign issue next year. “Vote for us to keep Trump in office!” will be the rally cry and the base will respond. At the same time a lot of the people who might otherwise have supported the DNC against Trump will not want to vote for what they will be 1-2 years of impeachment proceedings and little getting done.