Perhaps I'm issuing an open invitation for Phil to berate me with more attacks, but I believe this is the fundamental question for Republicans.
We have entire movements within the Republican Party that are dedicated to purging those within the Party who disagree with them.
33% of Americans identify themselves as conservative, and this number has remained stable for years. 50% of Americans identify themselves as moderate. With such a disparity in ideological self-identification, why would it make sense for the Republican Party to lampoon moderation (as Rush Limbaugh does all the time) and to systematically remove moderate Republican elected officials?
Becuase the Republican Party's greatest victories were with politcans like Reagan, and that people will vote Republican in the future because of Reagan not because of a big tent party.
Really that's what alot of populist conservatives use when talking about a bigger tent party.