Imagine if a group of antiwar Democratic senators had penned a letter to Saddam Hussein in 2003 saying, "Don't worry about President Bush's war threats. We will undercut him."

"Treachery!" Republicans would have roared. Yet 47 Republican senators, including Pennsylvania's Pat Toomey, have written an open letter to Iran's clerics saying Congress or the next president will probably rescind any deal signed by President Obama without congressional approval.

This effort to scuttle talks on curbing Iran's nuclear program is an extraordinary breach of tradition, providing the world with further evidence that the U.S. government is dysfunctional.

Even more bizarre, this appeal to the ayatollahs actually harms the effort to prevent Iran from obtaining a bomb.

The senators claim they had to act because Obama is pursuing an executive agreement rather than a formal treaty that would require two-thirds approval by the Senate. Yet, as the New York Times reported, 94 percent of accords between the United States and other countries since the 1930s have been executive agreements. (Backing out of such agreements would be an extraordinary breach of tradition.)

Moreover, the current nuclear talks are not just bilateral. They are being conducted by the permanent members of the U.N. Security Council - France, Britain, Russia, and China, with the addition of Germany, and with the United States in the lead.

U.N. involvement has made it possible to hit Tehran with global sanctions and will make it harder for Iran to break out of any agreement. (It will also make it tougher for a future U.S. president to dismiss any accord.)

That said, if greater congressional involvement is really what these senators want, they didn't have to write the letter. They could have waited until a framework pact was drafted and weighed in after seeing its terms.

There are indeed legitimate concerns about an accord: its length, any sunset provision, and Iran's coming clean on past weapons activities. Also, how fast sanctions should be lifted. The administration will have to listen to Congress since sanctions can't be fully lifted unless it approves.

But weighing in will require mastering Mideast details, not just lashing out at Obama. Republican critics have yet to offer a realistic vision of an alternative deal.

Most cling to a supposed alternative put forward by Israeli Prime Minister Benjamin Netanyahu in his controversial address to Congress. In a nutshell, Bibi proposed that Congress tighten Iran sanctions during negotiations and claimed this would force more concessions.

On the contrary, more sanctions right now would almost certainly scuttle the talks, in which case the international community would blame Washington for the failure, and the global sanctions regime would crack.

Never mind. Bibi says sanctions must be maintained until they force Iran to end its nuclear program and become a good Mideast citizen. In other words, hold out for a perfect agreement.

The Israeli leader knows this argument is nonsense.

Global sanctions, and low oil prices, did bring Iran to the table. But history has shown that if talks fail, Iran will ramp up its nuclear program despite sanctions. (Judging again by history, Tehran would probably stop just short of bomb production.)

In 2003, when George W. Bush spurned talks with Tehran, Iran had only 164 centrifuges, but it now has 19,000.

An interim pact put many of those centrifuges out of action, but an end to talks would, once again, set them spinning. That, in turn, would increase pressure from Republican hawks and from Israel for U.S. military strikes on Iran.

What neither Bibi nor the senators acknowledge is that such strikes would set Iran's program back by only two to three years. Unrestrained by global sanctions or inspections, Iran would probably race for an actual bomb. In the meantime, Washington would have become enmeshed in another Mideast war.

So it's time for those Republican senators to do some homework, and decide what they want.

Do they seek a realistic accord that would sharply curb Iran's nuclear program for 10 to 15 years? Or do they prefer a war that would halt it for two to three years and lead to a bomb?

Is their main goal to undermine Obama, or are they ready to work in a bipartisan fashion? If the latter, they'd better get briefed by experts. U.S. interests aren't served by evangelical hyperbole, whether American, Israeli, or Iranian.

And before they shoot off more letters, they should listen to Sen. Debbie Stabenow (D., Mich.), who invoked the late Sen. Arthur Vandenberg on the Senate floor. Although Vandenberg disagreed with FDR's efforts to squeeze Germany in the 1930s, "he did not send a letter to the chancellor of the Third Reich expressing his disagreements with the president," she said, her voice rising. In 1947, the Michigan Republican famously insisted "politics must stop at the water's edge."

"We can . . . disagree with the president," said Stabenow, but when "nuclear war hangs in the balance," we should not "be in the position of publicly undermining the president . . . to our enemies. I don't believe Senator Vandenberg would have become pen pals with a group of extremists. . . .

"It is shocking . . . that 47 members of this body decided to throw away 70 years of wisdom to stand on the side of . . . the most extreme voices in Iran."