U.S. Secretary of State John Kerry gestures while speaking at...

U.S. Secretary of State John Kerry gestures while speaking at a press conference at the end of the Iranian nuclear talks in Geneva on Nov. 10, 2013. Credit: AP

As Israeli Prime Minister Benjamin Netanyahu sees it, almost any deal between Iran and the West to limit Tehran's nuclear program would be a bad deal.

Before anything was finalized in Friday's nuclear talks in Geneva, the Israeli leader was already warning that a rumored accord was a "grievous historical error." He said Israel "utterly" rejected the accord, which would freeze much of Iran's nuclear program for several months in return for limited relief from international sanctions, while further talks sought permanent, verifiable curbs.

Netanyahu was jumping the gun, since there is no agreement yet.

But to the Israeli leader, the only deal that makes sense is one that totally ends Iran's nuclear program - full stop. He distrusts the dramatic overtures to the West made by the new Iranian president, Hassan Rouhani, and he calls for more draconian sanctions to be imposed on Tehran. His position has strong, bipartisan support in Congress, where new sanctions are under debate.

Before they rev up the pressure, U.S. legislators ought to consider whether an all-or-nothing stance toward Tehran will hurt U.S. and Israeli interests more than it helps.

After years of threats from Tehran and its Hezbollah ally, Israel wants to eliminate Iran's nuclear program, including a ban on any uranium enrichment, even for energy or research. But can such a maximalist deal be reached at the negotiating table? That is the question that must be honestly addressed.

"Not achievable," said Robert Einhorn, until recently a top State Department adviser on arms control. "I don't think any Iranian government could sell that deal at home," he added during a conference call hosted by the Israel Project, a nonprofit that promotes Israeli security.

While Rouhani and his team are willing to limit enrichment, they won't end it entirely. Einhorn believes that harsher sanctions would not budge them on this point, despite Rouhani's urgent desire to ease the burden of sanctions on Iran's economy. In conversations with numerous Iran experts, I've found widespread agreement with that view.

Instead, harsher sanctions at this point could halt diplomacy. Rather than curbing Iran's nuclear program, a breakdown in talks might well encourage Tehran to accelerate it, which has happened every time talks broke down in the past.

Moreover, Washington (and Israel) would likely be blamed for the diplomatic breakdown, with dangerous consequences. "I think we would pay a price in terms of the unraveling of sanctions," said Einhorn, "if it looked like we, and not the Iranians, were the cause of the impasse." In other words, harsher sanctions could boomerang.

In a fascinating speech to a top Israeli think tank in October, Einhorn suggested an alternative way of looking at negotiations. Titled "Is a 'Good' Deal Possible?" and available on the Brookings Institution's website, the speech should be required reading for members of Congress eager to tighten the sanctions screws.

The test of any nuclear deal, Einhorn suggests, should not be how it measures up to the ideal outcome, but how it compares with alternative means for dealing with the problem. If one accepts that sanctions can't end Iran's nuclear program, and one rules out diplomacy, there are only two other options: regime change in Tehran or war.

The American experience in Iraq should have ended any fantasies of imposing regime change on Tehran. As for a military strike on its nuclear facilities, the risks are substantial and the downsides enormous. For starters, a military attack would probably prompt Tehran to expel U.N. weapons inspectors and go full speed toward producing a bomb.

Do Iran hawks in Congress really have the stomach for another Mideast military expedition - especially when there is a chance of a diplomatic deal that would severely curb Iran's nuclear program and keep it under control? Which brings us back to Einhorn's basic point: The perfect deal is unobtainable. So can an agreement that falls short of ideal still be a "good" deal, one that is preferable to other options, even if it allows Iran to retain a limited enrichment program? That depends, of course, on the details. Any deal would ultimately have to cap Iran's centrifuge program and enrichment output, and prevent the start-up of the Arak heavy-water reactor. It would have to extend the breakout time - the point at which, should Iran ever kick out inspectors, it would have the fissile material for a bomb.

And any deal would require constant and intrusive inspections. It would also have to require Iran to come clean to U.N. inspectors about its past weapons programs.

This is a tall order. But, with Rouhani's election, a window of opportunity exists, and it would be foolish to waste it. The doubters in Congress should carefully consider the alternatives. And they shouldn't make the perfect the enemy of the good.

Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer.

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