The 47 Senate Republicans who warned Iranians against any nuclear agreement with Barack Obama that a Republican successor could revoke "with the stroke of a pen" billed their audacious letter to the clerical regime in Tehran as a civics lesson in the American constitutional system.

It has become instead an embarrassing testament to senators' ignorance not only of American constitutional practice but of the enforcement powers vested in the United Nations Security Council and vetted by the Senate when it approved ratification of the U.N. Charter seventy years ago.

GOP signers anticipated an outcry from the Obama administration; the president wryly remarked on the irony of "some members of Congress wanting to make common cause with hardliners in Iran." Some were a bit surprised by a broader public reaction--gauged less by the editorial pages of leading newspapers than by the fervor with which the blogosphere picked up the charge of "Traitors" leveled by the New York Daily News, of all newspapers.

Given Ayatollah Ali Khamenei's dark suspicions about "Zionist" control of the U.S. Congress, the letter's originator, Arkansas freshman Thomas Cotton, and his supporters could reasonably have supposed that their vow to undermine an executive agreement could flip the crusty cleric against the putative pact.

Khamenei is not known for a subtle mastery of international public relations, but the supreme leader's public reply Thursday had surprising resonance globally, particularly among America's European allies. The Republican senators' letter, he said, was "a sign of a decline in political ethics and the destruction of the American establishment from within." Far from turning against the nuclear talks, Khamenei reaffirmed support for his negotiators.

But it was Iranian foreign minister Javad Zarif who administered the coup de grâce to the pretensions of Cotton's constitutional tutelage. If an agreement is reached between Iran and the Security Council's five permanent members plus Germany, he said, it will be embodied in a Security Council resolution--enforceable under Chapter VII of the U.N. Charter.

Cotton seems never to have learned about the Charter while at Harvard Law School, and Zarif's reference apparently sailed over his and most other signers' heads. But Senate foreign relations committee chairman Robert Corker--who had pointedly refused to sign the Cotton letter--quickly realized that a Security Council resolution would render the Republican roadblock in Congress redundant. In a letter to Obama, he implored the president to indicate "whether you are considering going to the United Nations Security Council without coming to Congress first."

The answer is obvious, and Corker knows it. No member of the Security Council seeks its legislature's approval ahead of a vote in that body. The elder president George Bush went to the Security Council for a resolution approving military action to expel Iraqi occupiers from Kuwait months before he asked Congress for a war powers authorization to use American forces.

When the Senate debated ratification of the U.N. Charter in July 1945, the most troubling issue for many conservative senators was the legally enforceable character of actions the Security Council might take under Chapter VII. Would it allow a president to circumvent the Congress--and order U.S. forces into war without congressional authorization?

Seventy years later, the issue of the interplay between the Security Council and the Congress has returned, but with an ironic twist. The Security Council, it turns out, is much more of a brake on impulses to go to war than is the Congress. (Exhibit A: Iraq 2003.)

In the current case, the council's permanent members would be adopting a resolution to neuter Iran's nuclear program in order to avoid a war, while the demand of congressional opponents and embattled Israeli prime minister Binyamin Netanyahu for ending Iranian nuclear enrichment admits of one option only--war.

There is, to be sure, another irony. Speaking to the U.N. General Assembly in 1987, Khamenei himself, then president of Iran, derided the United Nations as a "paper factory" churning out "worthless resolutions." At the time, Iranians were incensed that the Security Council, in a shocking display of moral relativism, was calling evenhandedly for a ceasefire in the seven-year Iran-Iraq war rather than acting against the brazen aggressor in Baghdad who had launched it. But when the council finally imposed sanctions to compel an end to the fighting, supreme leader Ruhollah Khomeini was forced to "drink the bitter cup" of peace without justice.

U.N. sanctions have clearly brought home to Tehran the costs of its pursuit of nuclear threshold capabilities. If the "P5 plus 1" do conclude an accord with Iran, the Security Council resolution that lays out the timetable for implementing agreed controls over Iran's nuclear program will presumably prescribe as well the phase-out of the international sanctions regime. The Europeans, who have been the linchpins of the sanctions, will be as glad as the Chinese, Japanese, and Russians to end them.

At that point, hawkish congressional conservatives in Washington will be very much on their own. They can look to the success of their comprehensive, solitary, 53-year embargo against Cuba for their model.