For about a decade, the vast majority of Republican officials and voters were on the same page when it came to military force and national security. The line on the war in Afghanistan was especially clear — they attacked us on 9/11, the GOP has said, so we must stay until “the job is done.”

To put it mildly, that line isn’t nearly as bright as it used to be.

At this week’s debate for Republican presidential candidates, a voter asked whether it’s time to bring our combat troops home from Afghanistan. Mitt Romney, who endorsed the existing U.S. policy as recently as a few months ago, replied, “It’s time for us to bring our troops home as soon as we possibly can, consistent with the word that comes to our generals that we can hand the country over to … Afghan military to defend themselves from the Taliban…. I also think we’ve learned that our troops shouldn’t go off and try and fight a war of independence for another nation.”

The answer prompted Sen. Lindsey Graham (S.C.) to compare Romney to Jimmy Carter, and led to similar a rebuke from Sen. James Inhofe (Okla.). (Other conservatives marveled at Romney’s talk about Afghan “independence,” which doesn’t make any sense.) The Romney campaign spent much of the morning engaged in a “clean-up effort,” telling conservatives the candidate didn’t quite mean what he said.

While we wait for Romney to finish struggling with his own opinions, the larger point about Republican divisions on these issues is hard to miss.

The hawkish consensus on national security that has dominated Republican foreign policy for the last decade is giving way to a more nuanced view, with some presidential candidates expressing a desire to withdraw from Afghanistan as quickly as possible and suggesting that the United States has overreached in Libya.

The shift, while incremental so far, appears to mark a separation from a post-Sept. 11 posture in which Republicans were largely united in supporting an aggressive use of American power around the world. A new debate over the costs and benefits of deploying the military reflects the length of the conflicts in Afghanistan and Iraq, the difficulty of building functional governments and the financial burden at home in a time of extreme fiscal pressure.

The evolution also highlights a renewed streak of isolationism among Republicans, which has been influenced by the rise of the Tea Party movement and a growing sense that the United States can no longer afford to intervene in clashes everywhere.

And what happens when some of the GOP’s most influential voices on foreign policy oppose the agendas of the leading Republican presidential candidates? Will neocons bite their tongue out of a sense of party loyalty?

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.