Manchin is the ranking member of the energy committee = pork for his state. Vote to acquit = losing that perch. GOP Senators like Romney face no similar issues because McConnell is weak.
That, and he’s probably under a lot of pressure because he’s the lone Democrat in the Senate who isn’t a 100% loony-tune liberal, and his party wants very much for the vote to acquit to NOT be “bipartisan”.
So they give him this incoherent speech to read in order to to “explain” his vote, not figuring that anyone whose opinion matters will notice or care that the speech is pure idiocy.
No doubt, Schmukie wasn’t about to allow any defections. The rats didn’t fool around. You are right Mitch is weak. Yes he got the main goals done (no new witnesses and the Acquittal) but Schumer would not allow a punk like Mitt to embarrass their sitting President. No way.