The defections might be Jeffords-style without the caucusing. To me if we look at straight party line and assume that everyone in their party votes their party line, you are correct that it makes no sense to defect.
However, I think the dynamic of this next Senate will be different than previous. It is a VERY polarized (politically) Senate where moderates in both parties have left. In that environment, true power may come from a third group. If a centrist block is formed (and it seems the DLC is trying to accomplish this - although I am not sure how they are reaching out to Chafee and Snowe and other moderate Republicans) Chafee's influence will not be tied to his current party.
If the Dems gain two seats, and the Senate remains polarized, you can bet your farm that you will see overtures towards Snowe, Chafee.
"moderates in both parties have left. In that environment, true power may come from a third group."
That's the type of nonsense that poli sci profs would tell their students while still high from last night's party. It has no bearing on the real world, however.
Power in the Senate comes from holding the Majority. That's who chairs committees. That's who decides when to bring up "which" legislation and nominations. Moreover, it's the majority Party that decides on the final content of bills during the House-Senate conferences after all but the final voice votes are taken.
Buck the Majority party in the Senate and you lose your plum committee assignments. You lose your Party campaign funding. You lose support for your own legislation and nominations. In short, you lose.
So "power" doesn't come from so-called moderates who buck the Majority Party's Senate leadership.
If the Dems gain two seats, and the Senate remains polarized, you can bet your farm that you will see overtures towards Snowe, Chafee.Its been tried. Chafee simply won't leave (even though he is pretty liberal) out of family loyalty and some other various reasons. He also knows that switching can only cause him harm, based on the Jim Jeffords model. Snowe is to dependent on the GOP, and needs them more then they need her, the dems, do not have as much clout, and even in the most polarized situation, can offer nothing that would be less then what she has now.
McCain essentially turned down the sweetest deals of all. Kerry (source newsweek, and confirmed by various dems) offered him the VP slot, and in addition, total and absolute control over U.S. forign policy as also a position of SoD (McCain did point out this is unconstitutional). Everything but everything has been offered to McCain and he hasn't switched.
Those 3 individuals are the 3 canidates everyone always talks about switching. None of them will, and its clear now Specter won't either and in fact (out of fear) may actually harden a little bit now.
The GOP has effectivly brought up just enough margin to force its moderates more into line, the dems, have no way to keep theres in line. Even the DU'ers are pessimistic of taking back the senate anytime in the near future.