Ever since negotiators finished work on a nuclear agreement with Iran, President Barack Obama and his aides have been fending off critics with a recurring refrain: What’s the alternative?

“There’s no alternative that you or anybody else has proposed,” Secretary of State John F. Kerry lectured Sen. Marco Rubio, a Republican from Florida, last week.

“What’s the alternative?” Kerry asked earlier. “Go to war now?” In a column recently, I wrote that U.S. officials considered this their “killer argument.”

But Kerry was exaggerating. Plenty of conservatives have proposed alternatives to Obama’s Iran deal -- and not just war.

The simplest option -- and the one least likely to succeed -- has come from Rubio: Escalate U.S. sanctions until Iran cries uncle.

“The only option we have is to reimpose the American sanctions,” the Florida Republican said on CBS last week. “Give Iran a very clear choice: You can have an economy or you can have a weapons program, but you will not be able to have both.”

The problem is, U.S. economic sanctions alone have never compelled another country to surrender. And there’s little chance Obama or his successor could persuade the world’s other economic powers to join in sanctions if the United States walked away from the current deal.

Some conservatives have proposed a slightly more sophisticated option: Ask Iran and the other five countries in the negotiations to reopen the talks.

“The alternative is for Congress to reject this deal and demand a better deal, to send our negotiators back to the table with both tougher sanctions and (threats of) military force,” Sen. Tom Cotton, a Republican from Arkansas, said in a television interview.

“Arms control agreements are renegotiated all the time,” said Ray Takeyh, an Iran expert at the Council on Foreign Relations. “You just go back and say: We couldn’t get a bipartisan consensus. At that point, the Europeans and Russia and China have to decide whether to go back to the table too.”

That, however, is not as easy as it sounds.

“Do you think the ayatollah is going to come back to the table if Congress refuses this, and negotiate again?” Kerry asked. “I mean, please. I would be embarrassed to try.”

Kerry called it a “unicorn arrangement” -- “a fantasy, pure and simple” -- because international willingness to impose sanctions would erode, reducing U.S. leverage on Iran.

“I don’t think you’d see a total, utter collapse, but you’d see a crumbling,” Elizabeth Rosenberg, a former Treasury Department official who helped enforce economic sanctions, told me.

Even Takeyh, who favors this course, believes sanctions would weaken. “Yes, there will be leakage,” he said. “China may want to buy oil from Iran. India will want to reopen trade. It will mostly happen in Asia. But at least Iran won’t get access to the biggest markets.”

If the U.S. could keep Europe in line, he argued, Iran would come back to the table. That’s a big if, a European diplomat told me; French and German business delegations have already visited Tehran to look for new trading opportunities.

Finally, I’d be remiss if I failed to mention one last, bracing alternative to accepting the nuclear deal: military action against Iran.

Few of Obama’s critics promote that option, in part because U.S. military officials say it wouldn’t end Iran’s nuclear research, but merely set it back two or three years. Also, it could start a major war.

But one forthright proponent of airstrikes is John R. Bolton, who served as U.S. ambassador to the United Nations under President George W. Bush.

“If the real objective is stopping Iran from getting nuclear weapons, preemptive military action is now inescapable,” Bolton wrote in a column last week. “Some critics of Obama’s plan advocate scuttling the deal and increasing economic sanctions against Iran instead. They are dreaming .... There will be no other, better deal.”

That argument oddly puts Bolton in the same absolutist camp -- rhetorically, anyway -- as Kerry: If the deal doesn’t succeed, the most likely outcome is war.

So there are other alternatives. But none of them are easy, none are cost-free and none are guaranteed to work. If Obama’s deal with Iran is something of a gamble, his critics’ proposed alternatives are gambles too, and their outcomes would be even less certain.

By Doyle McManus

Doyle McManus is a columnist for the Los Angeles Times. Readers may send him email at doyle.mcmanus@latimes.com. --Ed.

(Los Angeles Times/Tribune Content Agency)