President Obama's nuclear deal with Iran presents an array of political challenges and opportunities for the Republican presidential contenders, while clarifying the foreign policy debate with Hillary Clinton in 2016.

Clinton, Obama's first secretary of state and the presumptive Democratic nominee, supports an agreement between Iran and the U.S. and other world powers to limit but not eliminate Tehran's nuclear weapons program. Virtually every Republican White House hopeful long ago promised to reverse course, should they succeed Obama in January 2017. With a deal now in place, Republicans say the contrast with Clinton is locked into place—and could not be more advantageous.

"Bad issue for the country; good issue for Republicans," veteran GOP strategist Ed Rollins told the Washington Examiner on Tuesday.

Obama addressed the country Tuesday morning, announcing that the U.S., negotiating with Europe, China and Russia, had reached an agreement to slow Iran's development of nuclear weapons, in exchange for billions of dollars in economic sanctions relief and the lifting of international arms embargoes. The president and other supporters touted the milestone deal with this hardened U.S. adversary as good for national security and the best Washington could achieve.

Some Democrats argue that voters in 2016 will ultimately come to appreciate the accord and warm to the new direction that Obama –– and Clinton –– has set for U.S. foreign policy, particularly as it pertains to America's leadership role in the Middle East cauldron. "This is an important step that puts the lid on Iran's nuclear program," Clinton told reporters on Capitol Hill, after a closed-door meeting with House Democrats.

It is precisely because Republicans doubt the agreement will halt Iran's determination to obtain a bomb and the means to deliver it that they are so confident in the party's hawkish opposition to Obama's détente with the Mullahs. Tehran will cheat, they are convinced, and the regime will continue sponsoring terrorist attacks against U.S. interests and allies, especially Israel. That will make Republican vows to pull the U.S. out of the deal an easy sell.

"When all the facts are out, the general electorate will oppose it. Clinton is in a box," said Charlie Black, a Washington lobbyist and veteran advisor of Republican presidential candidates. "A Republican president can charge Iran with violating the agreement — of course they will — and reopen negotiations to fix it, or get Iran to walk away from it. This deal has a half-life of about two years."

David Winston, a Republican pollster, said the debate hinges on whether Americans believe that Obama's deal prevents Iran from obtaining nukes. If general election voters trust that Tehran has been neutered, advantage Clinton. If they concur with the Republicans, that the Ayatollah pocketed concessions on his way to possessing a bomb, advantage the GOP nominee. A poll conducted before the deal was struck showed support for negotiations, but minimal faith that Iran would honor its commitments.

"If they think Iran is going to get a nuclear weapon, they'll be opposed to it," Winston said. "It's about one very specific thing, and that's unusual for the often gray areas we see in diplomacy."

The challenge for Republicans, if Iran behaves as they predict, is to offer a credible, detailed strategy for reining in Tehran in a post-deal world. Criticism alone won't convince voters that they have a workable alternative, or allow them to capitalize on voters' opposition to Obama's Iran policy, which is likely to become Clinton's policy unless she alters the support she voiced Tuesday.

Under the deal, the Europeans, Chinese and Russians are set to end their participation in the international sanctions regime that has hamstrung Iran's economy and motivated it to negotiate in the first place. Additionally, the United Nations is on track pass new resolutions legitimizing the agreement and ending treatment of Iran as a pariah state. That means that any Republican who might assume the presidency 18 months from now can't actually "cancel" the deal.

Under federal law, should Congress fail to muster a two-thirds vote of disapproval to overcome Obama's promised veto of legislation to block the deal, the White House has the power to wave U.S. sanctions on Iran by executive order. Either this president or his successor also has the power to unilaterally re-impose those sanctions, and that represents the breadth of what a Republican president could do on his own in January of 2017.

Clinton could argue to voters that, whatever their view of the deal, such a move could leave the U.S. isolated and in a weaker position to police Iran's nuclear ambitions. That's why it's imperative that the Republican nominee, whether a governor or senator, develops and comprehensive counterproposal to Obama's approach and clearly, and in practical terms, articulates how the U.S. reins in and re-isolates the Islamic Republic.

"It won't be enough to campaign against a weak deal," said Richard Grenell, a foreign policy analyst who advises Republicans. "Candidates need to explain how they will work with other countries to pass global sanctions again. Real and tough diplomacy is what is needed. It isn't enough to just have US bilateral sanctions. Candidates need to be good diplomats that lead the world."

That doesn't mean that the dogged rhetorical opposition expressed by Republicans —in Congress and on the campaign trail—isn't valuable.

Kori Schake, a research fellow at the conservative Hoover Institution who specializes in foreign and national security policy, said that American allies pay close attention to what is said in Congress and by political leaders of the party opposed to White House policy. They know that presidents come and go. For countries like Israel and Saudi Arabia, two vocal opponents of the Iran deal, hearing from Democrats and Republicans who remain suspicious of Iran, and hearing from potential Obama successors that they would pull the the plug on the agreement, can assuage their anxiety about the state of their relationship with the U.S.

"Other countries are really nervous about the Obama administration's choices," Schake said. "The concern being expressed in Congress and in public is incredibly reassuring to America's allies."

The Republican presidential contenders responded to news of the Iran deal swiftly and harshly.

Former Florida Gov. Jeb Bush derided it as "appeasement." Wisconsin Gov. Scott Walker said it would lead to a nuclear arms race in the Gulf. Former Texas Gov. Rick Perry said it was the "worst" foreign policy blunder of his lifetime. Former Arkansas Gov. Mike Huckabee said Iran is now "empowered to annihilate Israel, and Sen. Marco Rubio of Florida promised to re-impose sanctions if he is the next occupant of the Oval Office.

Their rhetoric, and the reaffirmation of their intent to shift U.S. foreign policy back toward muscular opposition to the Iranian regime, plays well with Republican primary voters.

The GOP electorate has expressed anxiety over the rise of the Islamic State and the renewed terrorist threat—not to mention Iran's threats to obliterate Israel—and have professed a desire for presidential leadership that reasserts aggressive U.S. influence in the Middle East and around the world. Foreign policy has emerged as an animating issue in the primary campaign, and the Iran deal is likely to ensure that international affairs remains at the forefront of the nomination fight.

"National security as an issue had already achieved an elevated status, registering with voters in the early primary and caucus states as the number two issue concern behind the economy," said a Republican operative who advised GOP presidential candidates in 2008 and 2012.

Disclosure: The author's wife works as an adviser to Scott Walker