Frist has himself backed into a corner here. Let me explain.
On one hand, he's retiring in 2006. This is his last hurrah as Senate Majority Leader. It's no secret that he's debating a 2008 nomination for President-the Republican field will be very open and Frist certainly has the name recognition down to make a run for it. HOWEVER, he hasn't really endeared the conservative base during his time as majority leader. He's been unable to get anywhere on the social conservative agenda-he's a workaholic, but he's was consistently outflanked by Tom Daschle before this Congress and is already losing some fights in this Congress as well, in large part due to his inability to fragment and peel off Democrats while losing a couple of Republicans.
Essentially, he's not viewed as someone who served in Washington at the crest of Republican power and enabled the kind of sweeping reform with the majority that the base would have liked.
Now he's got the chance to redeem himself in the eyes of the GOP faithful by making a VERY public power grab and sending the most blantant of parlimentary FUs to Democrats by abolishing the judicial filibuster. It has wide conservative base/activist support and will get him tons of good press in the ring wing media for doing so, even if it comes at a steep cost. If it means that the Senate can install a Bush-selected wingnut SC justice with 50 votes, they'll be estatic with him, regardless of the irreperable damage done to the Senate and the parlimentary standstill that will occur afterwards.
Going nuclear seems to be the way for Frist to leave office with a bang and set himself up well to run in 2008 if that's what he wants. If he doesn't want to run in 2008, it's likely that he deliever the rules change and will instead kindly ignore the Bush re-nominees while the Democrats filibuster them down again.
It's a tough spot for him. Without going nuclear, I don't see how he finishes in the top five in Iowa or South Carolina in the 2008 primaries.