After years of negotiations, President Obama has announced the successful and historic conclusion of a nuclear arms deal with Iran.

Immediately, his opponents here in the United States announced that they would do everything possible to undermine the deal, just as hard-liners in Iran are doing. Several Republican presidential hopefuls have announced that, if elected, they would unilaterally abandon the deal as soon as they took office. Such rhetoric all but guarantees that Iran will be a major campaign issue throughout the 2016 campaign, which is fine. It ought to be.

So let’s think this through. If a Republican takes office on Jan. 20, 2017 and immediately withdraws from the deal, as promised, what happens?

It’s pretty straightforward: Iran would kick out the international inspectors, which means that we would lose almost all insight into Iran’s program. Some 13,000 of Iran’s most sophisticated nuclear centrifuges that are mothballed under the deal would be returned to service, once again producing the highly enriched uranium needed to build bombs. The allies with whom we have worked hard to negotiate the deal in good faith will feel betrayed. China and Russia, which have been part of the deal as well, will have every excuse for refusing to cooperate further.

Nonetheless, GOP candidates claim that after abandoning the deal, they would replace it by once again instituting tight economic sanctions against Iran. But they have almost no chance of doing so. The tight sanctions that have forced Iran to surrender 98 percent of its low-enriched uranium and agree to international inspections were possible only because we had the cooperation of most of the world. If the United States unilaterally abandons this deal, Iran would be able to portray itself as the country that abided by international agreement, while we would be the rogue nation that broke it. Under those circumstances, we would have no chance of getting international cooperation for a new set of sanctions.

With no possibility of meaningful international sanctions, our sole remaining option to keep Iran from going nuclear would be another destabilizing war in a region already destabilized by a previous ill-considered war. And the only way to ensure that we have destroyed Iran’s nuclear capability and to ensure that it does not restart its program would be to invade and permanently occupy the country, a task that would make the occupation of neighboring Iraq look like a picnic.

Critics of the Iran deal focus on the things that it does not do. They point out, correctly, that it doesn’t end Iran as a potential source of terror, as a threat to Israel and the Gulf States, or as a regional competitor to the United States. Nor does it remove Iran’s theocratic government. Worthy as those goals may be, however, they are all well outside the realm of a nuclear arms control negotiation.

The goal of the negotiations has been to halt Iran’s nuclear program, to force Iran to undo much of the progress that it had achieved toward a nuclear weapon, and to open its program to long-term international inspection. Those goals have been achieved. In short, the 2016 presidential campaign will become a referendum: War or peace?