Given the reality of party primaries, and the fact that each candidate raises his own funds, mainly from the conservative grass roots, I'm a little confused as to how anyone can purge conservative Republicans from congress.
There is not only official endorsement, but also voters lists, soft money, and party organization. Added up, it is a huge bonus for an endorsed primary candidate.
In the primaries of the last election, it took an enormous amount of grassroots effort and outsider organization to overcome such endorsements. The party openly supported incumbent RINOs and went so far as to disparage Tea Party candidates.