If U.S. and European nuclear negotiators hoped a more tractable government would emerge in Iran after presidential elections in June, those hopes have faded. Election authorities have disqualified two maverick candidates; the remaining eight are in the conservative camp of Supreme Leader Ayatollah Ali Khamenei.

Under Khamenei, Iran has shown limited interest in multilateral negotiations to restrict its nuclear program. Meanwhile, according to a new International Atomic Energy Agency report, the country has expanded its capacity to produce enriched uranium and plutonium, both of which can fuel bombs.

Seen in that context, legislation being considered by the U.S. House of Representatives to increase already strong sanctions on Iran might seem prudent and appropriate. Promoting the measure before the Foreign Affairs Committee he leads, the bill’s sponsor, Republican Ed Royce of California, rightly argued that preventing Iran from acquiring nuclear weapons is of the highest priority. Royce also said, “We have to play every card and pull every lever we have.”

Actually, as Kenny Rogers advises, that’s no way to play cards. It’s also a recipe for diplomatic failure.

Yes, piling sanction on top of sanction has increased the cost to Iran of pursuing its nuclear program in violation of its IAEA obligations. Targeted sanctions have slowed Iran’s nuclear progress. Punitive sanctions, like the ones before the House, have damaged its economy.

Yet Iran isn’t going to unilaterally change its nuclear policies in the mere hope that doing so will bring some sanctions relief. A sanctions strategy will work only if Iran can be promised the penalties will end if its policies change.

Most U.S. sanctions on Iran are executive orders, which the president can lift. Those few mandated by Congress, however, can be reversed only by new congressional action. That limits the ability of U.S. negotiators to offer sanctions relief in return for Iranian concessions. Royce’s bill, which tightens existing sanctions on Iran’s oil exports and limits its access to foreign currency reserves abroad, would add to that complication.

Members of the Foreign Affairs Committee, who unanimously recommended the bill for the House’s consideration, seem to think more sanctions will provoke more concessions. The opposite may be true. Ayatollah Khamenei already appears convinced that regime change is the goal of U.S. sanctions and is thus wary of nuclear diplomacy. The Royce bill may only deepen his skepticism and stiffen his resistance.

Before running that risk, the U.S. should, with its allies, test whether it can induce changes in Iran’s behavior by using existing penalties, such as United Nations Security Council restrictions on Iranian banking, a European Union oil embargo and an almost complete economic embargo by the U.S., including sanctions on companies that do business with Iran.

In recent talks, Iran appeared to consider limiting its stockpiles of 20 percent enriched uranium, suspending production of the stuff at its fortified facility at Fordow and accepting tougher IAEA monitoring of enrichment sites. In the end, it decided not to do so. Its refusal was no great surprise: The benefits it stood to get -- relaxation of a ban on trade in precious metals and an easing of an embargo on its petrochemical products -- were hardly commensurate.

Once a new president is installed in Tehran, the negotiators from China, France, Germany, Russia, the U.K. and U.S. ought to propose an action-for-action road map, laying out all the sanctions they would lift in exchange for all the nuclear concessions they want from Iran.

The Westerners should state from the outset that once Iran is in full compliance, they will accept its limited right to enrich uranium. A right to enrich is a sine qua non for Iran, and its absence has been a stumbling block. Once that’s removed, the two sides can negotiate the order and magnitude of reciprocal actions.

If that diplomacy fails, greater penalties -- including limits on Iran’s access to foreign-currency assets abroad -- may be required to encourage Iran’s assent. Still, only as a last resort should Congress force the president’s hand. As the negotiator-in-chief, he needs to retain the power to turn the stick of sanctions into the carrot of relief.

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