@mpjgregoire Schumer, Pelosi, and Jeffries all visited him and recommended he step down. Apparently Pelosi was getting ready to play hardball.
That, plus the ever-growing tide of elected Dems calling for the same made it an inevitable decision.
Also, it wasn't sudden at all. He had been considering it for a while now, but they had to maintain the appearance of strength, so they couldn't say that until after he was out.