Marco Rubio didn't run on a platform that included getting out of Afghanistan, abolishing the TSA, and opposing the NDAA while appearing with Ron Paul. Ted Cruz did. In an interview with me, Mike Lee criticized the Libya war on substantive as well as constitutional grounds and didn't sound too enthusiastic about our other recent wars. Although Jim DeMint voted for the Iraq war, he was also one of just four Senate Republicans who voted to end its authorization.
Look, these candidates aren't noninterventionists (although a few of them, like Thomas Massie and Kerry Bentivolio, essentially are). But in the not-too-distant past, the most conservative candidates running in a Republican primary would have been without fail the most enthusiastic champions of the Bush Doctrine and dead-enders in support of unpopular foreign wars. The fact that these candidates don't fit that description doesn't necessarily mean they will be cautious on Iran, but it does mean something.