The two rats in question are Senator Domenici, who will have a real challenge for re-election next year. Reid has effectively challenged Domenici to put his votes where his mouth is next week, at which point Domenici might cave.
More interesting still is John Doolittle. Given the number of close Doolittle staffers who have been interviewed by the FBI of late, I expect the seemingly inevitable indictment against him will be very aggressive. Now perhaps this Doolittle trial balloon (ha!) is going to be about as effective as the similarly legally threatened Ted Stevens' vote of present on the no confidence vote against Alberto Gonzales: that is, not a voice in favor of Bush's guy, but not effectively a vote that does the same thing anyway.
The most interesting thing about this, though, is not any real dissatisfaction from Republicans with Bush's imperial war (I'm not holding my breath). But the use of the war as currency with which you can get distance from Bush--or pressure him.