The answer to many of those questions boils down to the sheer amount of power held by the minority leader. So much of what the senate does is done by unanimous consent, and the minority leader essentially has as much power as the majority leader, except with regard to what comes to the floor. They could gum things up so badly, and the only reason they don't is the threat of retribution from their counterpart when their fortunes are reversed. Much should be modernized about the senate (electronic voting with correspondingly streamlined voting timelines, elimination of cloture votes at least when the threshold is 50), and having Manchin out of the caucus will make achieving that easier. We shall see in the coming years who the next rung of remaining traditionalists are.