The international community’s sanctions on Iran have been very effective. That approach remains the most likely method — short of military force — of persuading Iran to stop defying the United Nations Security Council’s demand that it give up its quest for nuclear weapons.

Tuesday’s Wall Street Journal reported that Iran’s state-owned natural gas company is facing bankruptcy because it cannot obtain foreign capital. Reuters reports that Iran’s oil exports have fallen 60 percent. The nation’s currency has collapsed against the dollar, the costs of basic necessities of life are soaring, and inflation there has reportedly soared to 40 percent.

There is no question that Iran has agreed to negotiate a retreat from its nuclear programs because it is seeking relief from these sanctions.

President Barack Obama wants to ease the sanctions on Iran while approaching an accord to stop its advance toward a nuclear arsenal.

And New York Times columnist Thomas Friedman, on today’s Commentary page, argues that it is in the best interests of both the U.S. and Israel to reach an agreement with Iran.

But what happens if Iran signs such a deal, then violates it?

Or what happens if no deal is reached? After all, several previous negotiations with Iran have failed.

President Obama says that Iran doesn’t meet the terms required to prevent it from developing nuclear arms, the nations negotiating with it will simply ratchet up sanctions back to their current levels — or higher.

But such a decision to reinstate sanctions is not assured. For example, the European Union’s trade with Iran, which is roughly 50 times larger than American’s trade with Iran, has fallen by about half since 2005. If relaxing sanctions allows this trade to increase toward previous levels, European governments facing high unemployment will have a difficult time restoring the sanctions if a final deal with Iran proves elusive.

Other nations negotiating the deal with Iran include Russia and China, both eager to expand their trade with Iran.

So if a breakdown in negotiations leaves Iran in control of its nuclear options, the United States could find itself isolated in calling for a restoration of sanctions.

A large number of U.S. senators, including South Carolina Republican Lindsey Graham, advocate increasing the pressure on Iran until it agrees in a verifiable deal to give up its capabilities to acquire nuclear weapons. But they have accepted President Obama’s plea that they hold off legislation to toughen sanctions for the time being.

Still, the president should heed the senators’ warning. He will be held responsible if he goes ahead with a deal that lets Iran partly off the hook for little more than a promise of future cooperation.

That is a very risky course, and one that would be difficult to reverse.