Knight Ridder had a story yesterday on Sen. Bill Frist's barely-hidden ambition to run for the White House in 2008. He's already making trips to New Hampshire, and decided not to run for reelection to the Senate in 2006.
How can Democrats use this against him? IMO, they need to define his image now as a partisan hatchet man in order to undercut his '08 prospects (and the inevitable effort to remake his image as an outsider). As a side benefit, simply launching the assault will make him more cautious in pushing the Dubya/wingnut agenda -- thereby helping Democrats derail more of it.
For further explanation, see my post on this at Needlenose. (NOTE: In the comments, I see a lot of people saying, "Nah, don't waste the time, Frist is a sure loser in '08" ... but isn't this what we all thought about Dubya?)