They want to impeach him not to put Pence in office but to prevent facing him in the 2020 election and possibly losing the house at the same time. While both Warren and Sanders are the cats ass in Ca. and New York but their free bullshit does not play well in the swing states.
Not only did they already say they'd go after Pence next, but they would punish Trump voters. Leftists are the creators of gulags and shouldn't be treated as human. They're evil filth who should be wiped off the planet, as the scourge they are.