For most Republican presidential candidates, opposing the nuclear deal with Iran is a political no-brainer. Whatever the merits of the agreement, supporting it requires asking a GOP primary electorate to trust Barack Obama, John Kerry and ayatollahs in Tehran. Earlier this year, Gallup found that 91 percent of Republicans viewed Iranian nuclear weapons as a critical threat.

Many of the libertarians, realists and noninterventionists who back Rand Paul or supported his father take a different view of the nuclear deal, however. They see it as a repudiation of the Bush Doctrine and a victory of diplomacy over yet another war in the Middle East. An April Reuters poll found nearly a third of Republicans favored the then-incomplete agreement.

The junior senator from Kentucky announced late Tuesday that he wasn't one of them. He argued that the deal struck by the Obama administration and U.S. allies was too weak and did not do enough to prevent Iran from acquiring nuclear weapons, so he would vote against it. Some libertarians, regarding this as a concession to neoconservatives and other hawks, were not pleased.

"Rand opposes peace with Iran," blogged Lew Rockwell, a former congressional chief of staff for Ron Paul who used his eponymous libertarian website to boost the elder Paul's 2008 and 2012 presidential campaigns. "He sides with [Israeli Prime Minister] Bibi [Netanyahu] and other death merchants."

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Most critics didn't go as far as Rockwell, but it was the culmination of libertarian discontent with Rand's Iran stance since he signed Sen. Tom Cotton's letter to Iranian leaders in March. Paul's detractors fear that the 2016 presidential campaign has turned him into a conventional Republican hawk.

Paul has tried to emphasize that he wants to stick with the interim agreement and continue negotiating with Iran and trying to get a better deal, unlike other Republicans who are talking about things like an authorization of military force. His camp says they took longer than most Republican candidates to react publicly because they were open to supporting a deal if it was good enough and were reviewing the details.

A source close to Paul disputed the idea "that you must support this particular deal or you are for war," comparing it to claims that one must either support an activist foreign policy or oppose a strong national defense. Ultimately, those close to Paul say the deal as presently written doesn't do enough to verify Iranian compliance to be worthy of support.

Trust but verify. The phrase was at the heart of Ronald Reagan's negotiations with the Soviets and Paul believes it is the key to a better deal with Iran. Will that be the attitude of libertarians and anti-interventionists toward Paul on foreign policy?

Jim Webb, a passionate Iraq war opponent who rejoined the Democratic Party because he thought neoconservatives had too much influence in the GOP and who sought to block preemptive military strikes against Iran while in the Senate — has also been critical of the deal. At this writing, no major libertarian-leaning Republican in Congress has endorsed it. Rep. Mark Sanford, R-S.C., issued a skeptical statement Tuesday.

This isn't the first time Paul has sparred with the base he inherited from his father on these issues. He came under fire when he voted to temporarily filibuster Chuck Hagel's nomination for secretary of defense. Hagel had been a rare Republican critic of the Iraq war late in his Senate tenure.

"You would think by some of the comments I get that Hagel is really [two-time Libertarian Party presidential nominee] Harry Browne," Paul complained. "They make him out to be some sort of libertarian champion, and he's not."

Paul later voted to confirm Hagel, whose impact on the Obama administration's foreign policy was minimal. But what subsequently returned libertarians and antiwar conservatives to the fold was Paul's filibuster of CIA director nominee John Brennan over drones.

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Many who were angry with him over his procedural votes on Hagel opted to enthusiastically "Stand with Rand" on drones. So did some establishment Republican senators who likely wouldn't have if Paul had cast the deciding cloture vote for Hagel.

A similar dynamic was seen after Paul supported limited strikes against ISIS in Iraq and introduced an amendment that would have increased defense spending, provided there were offsetting spending cuts elsewhere. His liberty movement base was upset, but most of them rallied behind his efforts to force the expiration of sun-setting surveillance provisions of the Patriot Act.

Will those who are disappointed by Paul's opposition to the Iran deal stand with Rand again when he comes under attack from more hawkish rivals like Chris Christie and Lindsey Graham? Or will they follow Paul's advice to the Obama administration on Iran and try to get a better deal by showing a willingness to walk away?