Either way this plays out I dont see it being a + for the democratic party. I think D leadership already knows they are shit out of luck for 2020 and are sick and tired of listing to the squad bitch and moan. By allowing this vote Nancy shuts up the 60-70 vocal impeacher congress members (who by the way have been after this since literally the morning after the 2016 election), appeases the impeacher voters, and gives the media the impeachment soap opera they are all drooling over.
In the end this will hurt the D party as a whole, Trump is at 48%-53% approval depending on who is polling. So around 50% of the voters favor Trump, and Americans are by culture dont like people being treated unfairly. Over the year the Trump rally's will double in size, MAGA hats are going to proliferate well into main stream, and any house and senate D members out for reelection in purple states are most likely already looking for new employment opportunities stating first of February 2021.
Remember kids, being but hurt about an election is not a reason to pull a stunt like this.