Ed Gillespie explained to me ages ago that the party "is" the incumbents (of the incumbents, for the incumbents). If it was not, it wouldn’t be the party (we’re far removed from the 1800’s smoke-filled rooms with a cabal operating thru the incumbents). Which is why a party will never support a challenger in a primary (it can’t and survive).
Which is why we need folks like The Club For Growth and now the Tea Party to drive change. Elting Morrison (the first non-engineer at MIT) observed that only external forces can change a closed society. And that this change doesn’t come easy.