Wait until they are up for re-election. One month before primary date, kick them out of the party and run a real republican candidate.
Let’s see if they can mount an independent run like CT Senator Lieberman, only talk them down significantly.
Snowe, Collins and Spectre. They need to be kicked to the curb.
Funny you mention Specter, that is where I live now. I am trying to fix it down here.