A couple of observations. First it will be interesting to see how Nancy finesses this. I’m not so sure she saw this one coming. She figured that Van Drew would be a “no” vote and she could spin that by saying that she wants everyone to vote their conscience, yada, yada. Changing parties is a whole ‘nother thing.
Second, Van Drew’s move is crass, self-serving chickenshittery. If his conscience won’t allow him to vote for impeachment then vote no, or just quit. My guess is that he wants to fill out his term so he can collect the pension.
I suspect there's more to it than that. See Post #23 in this thread from earlier today: