Arlen Specter, Republican Senator from PA who was one of three Republicans to vote for the stimulus bill, describes a conversation with another Republican senator who voted ‘no’:
“When I came back to the cloak room after coming to the agreement a week ago today,” said Specter, “one of my colleagues said, ‘Arlen, I’m proud of you.’ My Republican colleague said, ‘Arlen, I’m proud of you.’ I said, ‘Are you going to vote with me?’ And he said, ‘No, I might have a primary.’ And I said, ‘Well, you know very well I’m going to have a primary.'” Huffington Post
What he is talking about here is the primary election pressure that is and will be brought to bear on any sitting Republican in Congress or Senate who fails to vote in accordance with the wishes of the extremist elements in the party. Insufficient ideological purity means somebody to the right of you will challenge you in the primary and that challenger will have the advantage of big pots of money and organizational support to the end of defeating you, you heretic.
Further, what are effectively propaganda campaigns waged against such moderates will commonly be directed by someone(s) like Grover Norquist who will engage the assistance of local and national talk radio (and other such outlets) to magnify and echo the attack. What makes such a dynamic relatively easy is that primaries bring out a very small percentage of the Republican voters in any region and those folks are mostly the serious activists (read, the more extreme party members) who take their cues from talk radio and other such voices. See the following for a fine example: Specter is Porker of the Year
In his last primary battle, Specter barely beat out a far more radical challenger who had been supported in precisely these ways.
And, if you were to put “Grover Norquist” on a google news alert (as I have) you’ll get a good idea of just how active this guy is across the country at federal and state levels pushing his party to its modern extremes.
Update: As a case in point, see Charlie Crist has impure thoughts