In primary campaigns where there’s not much daylight on policy between establishment Republicans and conservative challengers, how willing a candidate or incumbent was to close the government – and opposed to a compromise on Obamacare that would reopen it – looks like the base’s latest test of who’s a true believer or a squish. And for Republican elders who were urging an end to the intra-party warfare that cost the GOP Senate seats the past two election cycles, it’s another reminder the party isn’t remotely close…

“Anyone who has a tough primary is kind of cowed into holding the line,” said a Republican who managed a Senate campaign last year. “It’s a scary thing to stare down that gun when you’re trying to win a race. The gun seems to be getting more powerful.”…

Republican strategist Brian Walsh said attacking more establishment-friendly Republicans from the right on the shutdown may backfire.

“The argument could cut both ways,” said Walsh. “Let’s start from the predicate that there will have to be a compromise, which some of the outside groups will oppose. On the one hand, you’ll have outside groups demanding purity. On the other hand, you go too far and risk not being seen as a serious leader.”