suggests Dem leaders think moving toward impeachment endangers their chances "to retake the House and... maybe even the Senate."
I take a longer view. The only way to get anything done anymore is to control White House, House, and Senate. (This is true for the Dems, at least, because of Republican obstructionism--I hope the Dems have learned enough (and care enough) to make this true for Republicans, too, but I doubt it.) My eyes are on 2020. Most voters in recent U.S. elections, I think, vote against
something more than they see either party as offering them anything to vote for
. The more directly the Dems attack Trump, and the more power they have to do so, the more they energize Trump's base. I hope that in 2018 the Dems pick up seats but fail to retake either house.
P.S. Even if Dems retake WH and Congress, because the right wing is now filling the judicial openings they refused to let Obama fill, for a good long while the courts will be an obstacle to some reforms.