Joe Manchin is from West Virginia, a highly conservative state. Nancy Pelosi and Chuck Schumer didn't put him in office; his rural, under-educated, consesrvative constituents put him in office, and they're going to keep him there, no matter how much he votes against their interests.
No one with any sense believes that Joe Manchin is a liberal. He doesn't care what liberal Democrats have to say about him, and neither do his constituents. He doesn't have to worry about running again for four years. No matter how much we complain or wish it otherwise, we're not going to get a liberal or an activist in West Virginia. If we keep insisting that it is so, then we're naive as hell and don't know how politics works. It's better to concentrate on races we can win; then we can make Manchin irrelevant.