So far, he always acts like he needs the Democrats' approval before he does anything.
He does.
The ability (and willingness) to destroy something is the power to control it. The Democrats are willing to destroy our government if they're not in charge. Frist isn't willing to let that happen, therefore he is hamstrung. His biggest weapon was the "nuclear option" and John McCain and the 6 other RINOs took that away from him. It's kinda hard to lead a movement when you're constantly being stabbed in the back.
Now, Mitch McConnel is the type who might just turn around and kill a few of his more mutinous troops were he Majority Leader, as a kind of example, if you get the drift. It's not in Frist's nature to do that, which is why he never should have been Majority Leader.