A Bad Night for John McCain
Lieberman loses and is thown out of the party. In MI-07, McCain-endorsed Joe Schwarz is booted by a conservative primary challenger. Primary voters tire easily of mavericks.
I'll tread lightly on what these primaries mean for good or ill, because a rejection of a "moderate" like McCain can also mean the rejection of a "moderate" like Rudy. But I think we can cautiously assume that hardcore, ideological primary voters (and they're even more hardcore in off-years) will accept a more "moderate" nominee (Baar-Topinka in IL, Corker in TN) who is perceived as absolutely loyal to the party. If you generally vote like a liberal but cross your party on an issue of fundamental importance (Lieberman on Iraq = McCain on immigration and taxes) or if you actively campaign as a RINO (Schwarz), you lose. If Rudy tries to act like a maverick or play the moderate, I'll be much more sanguine about his chances.
And to Gary, no, this doesn't mean Giuliani is a liberal, only that he will be attacked as such and we should be prepared. The 2006 Republican primary season provides clear guideposts for when those charges stick and when they don't.