Over the past centuries, Western diplomats have continually projected pragmatism onto their ideological opponents. They have often assumed that our enemies are driven by the same sort of national interest calculations that motivate most regimes. They have assumed that economic interests would trump ideology and religion . that prudent calculation and statecraft would trump megalomania.

They assumed that the world leaders before 1914 would not be stupid enough to allow nationalist passion to plunge them into a World War; that Hitler would not be crazy enough to start a second one; that Islamic radicals could not really want to send their region back into the 12th century; that Sunnis and Shiites would never let their sectarian feud turn into a cataclysmic confrontation in places like Iraq.

The Obama administration is making a similar projection today. It is betting that Iran can turn into a fundamentally normal regime, which can be counted upon to put G.D.P. over ideology and religion and do the pragmatic thing.

The Iran nuclear negotiations are not just about centrifuges; they are about the future of the Middle East. Through a series of statements over the last few years, President Obama has made it reasonably clear how he envisions that future.

He seeks to wean Iran away from the radicalism of the revolution and bind it into the international economic and diplomatic system. By reaching an agreement on nukes and lifting the sanctions, Iran would re-emerge as America’s natural partner in the region. It has an educated middle class that is interested in prosperity and is not terribly anti-American. Global integration would strengthen Iranian moderates and reinforce democratic tendencies.

Once enmeshed in the global system, Iran would work to tame Hezbollah and Hamas and would cooperate to find solutions in Gaza, Iraq and Syria. There would be a more stable balance of power between the major powers. In exchange for good global citizenship, Iran would be richer and more influential.

To pursue this detente, Obama has to have a nuclear agreement. He has made a series of stunning sacrifices in order to get it. In 2012, the president vowed that he would not permit Iran to maintain a nuclear program. Six United Nations Security Council resolutions buttressed that principle. But, if reports of the proposed deal are correct, Obama has abandoned this policy.

Under the reported framework, Iran would have thousands of centrifuges. All restrictions on its nuclear program would be temporary and would be phased out over a decade or so. According to some reports, there will be no limits on Iran’s ballistic missiles, no resolution of Iran’s weaponizing activities. Monitoring and enforcement would rely on an inspection regime that has been good, but leaky.

Meanwhile, the United States has offended its erstwhile allies, like Israel, Saudi Arabia and Egypt, without being sure that Iran is really willing to supplement them. There is a chance that Iran’s regional rivals would feel the need to have their own nuclear programs and we would descend into a spiral of proliferation.

All of this might be defensible if Iran is really willing to switch teams, if religion and ideology played no role in the regime’s thinking. But it could be that Iran has been willing to be an international pariah for the past generation for a reason. It could be that Iran finances terrorist groups and destabilizes regimes like Yemen’s and Morocco’s for a reason. It could be that Iran’s leaders really believe what they say. It could be that Iranian leaders are as apocalyptically motivated, paranoid and dogmatically anti-American as their pronouncements suggest they are. It could be that Iran will be as destabilizing and hegemonically inclined as all its recent actions suggest. Iran may be especially radical if the whole region gets further inflamed by Sunni-Shia rivalry or descends into greater and greater Islamic State-style fanaticism.

Do we really want a nuclear-capable Iran in the midst of all that?

If the Iranian leaders believe what they say, then United States policy should be exactly the opposite of the one now being pursued. Instead of embracing and enriching Iran, sanctions should be toughened to further isolate and weaken it. Instead of accepting a nuclear capacity, eliminating that capacity should be restored as the centerpiece of American policy. Instead of a condominium with Iran that offends traditional allies like Saudi Arabia, Egypt and Israel, the U.S. should build a regional strategy around strengthening relations with those historic pillars.

It’s hard to know what’s going on in the souls of Iran’s leadership class, but a giant bet is being placed on one interpretation. March could be a ruinous month for the Middle East. Prime Minister Benjamin Netanyahu of Israel could weaken U.S.-Israeli relations, especially on the Democratic left. The world might accept an Iranian nuclear capacity. Efforts designed to palliate a rogue regime may end up enriching and emboldening it.