If the dems come out of this without a single repub vote in either the House or Senate, it's a crushing defeat that will go down in history as colossal hyper-partisan overreach. Losing even one dem senator on top of that would be an unmitigated disaster. That's why I say they had to have made sure Manchin's vote was locked up before they took it this far. I'm not sure how far gone Pelosi's mind is, but she's not that senile yet.
If you think about it, Schiff's failure to make a dent in public opinion might have made Manchin skittish, and that might well have been the real reason for Pelosi's delay in sending the articles. Maybe only when this "new evidence" appeared were they were able to squeeze a commitment out of him.