Having rounded this off with a call for the U.S. to place itself in the service of his brand of "multilateralism," d'Escoto demanded "a united nations, not a subjugated nations." After 45 minutes of this, delivered in a soft, lilting voice, he removed his substantial girth from the press room stage, presumably to carry on with his duties from his lavishly furnished office overlooking the East River.

It might be tempting to dismiss this performance as just one more case of the U.N. buffoonery to which Americans have become accustomed, just another item for the Turtle Bay scrapbook, a lesser variation on such historic histrionics as Nikita Khrushchev pounding his shoe and Yasser Arafat wearing a gun holster. After all, does the U.N. really matter?

Yes. The U.N. matters a lot. And it matters for reasons much bigger and more disturbing than America's billions in outsized contributions poured every year into the U.N.'s murky coffers, though it does bear noting in d'Escoto's case that the financial arrangements are intriguing. The U.S. pays the lion's share of the cost for his fancy facilities in New York, but apparently U.N.-sanctioned Iran picked up part of the tab for his trip to Tehran.

My queries about who paid for the recent trip were answered by d'Escoto's spokesman, with an e-mail message that said, "The entire trip was paid" by "the countries he visited, except the two days staying in Geneva … as for the air travel, each country provided the air tikets [sic]."

That raises some interesting ethical questions about whether the president of the U.N. General Assembly should be accepting such frills as air tickets from member states, as well as how, exactly, the payments were arranged, or logged in by U.N. book-keepers. Neither d'Escoto's office nor Iran's Mission to the U.N. replied to my follow-up questions about these matters.

But for a handle on the larger problem with the likes of d'Escoto, and his activities under the U.N. logo, let us turn to an important essay published in 1989 by a former U.S. Ambassador to the U.N., Jeane Kirkpatrick. Writing in Commentary, Kirkpatrick explained "How the PLO Was Legitimized." The gist of her eight-page article was that it was done through the U.N., by way of "international diplomacy--reinforced by murder."

In richly documented detail, Kirkpatrick chronicled how, when Israel's military victories in 1948, 1967 and 1973 "made the price of large wars too high," Arab states moved their struggle to the U.N.: "An arena whose chief activity is not conflict resolution (as is generally believed) but what has been correctly termed 'collective legitimization' and 'collective delegitimization.'"

Such exploitation of the U.N. proceeds by way of appropriating vocabulary (such as "holocaust"), twisting words or emptying them of any real meaning (such as "terrorist," for which the U.N. still has no agreed-upon definition), staging conferences that import select initiatives into the U.N. agenda and introducing resolutions that craft what is presented as "world opinion," to be translated into effect on policy and international law.

While Americans were prone to dismiss many of the U.N.'s doings as mere semantic battles, Arafat and his colleagues knew better. Kirkpatrick explains: "They recognized the U.N. as a political opportunity and knew how to grasp it. They devised tactics for practicing the distinctive brand of bloc politics that passes for diplomacy in multilateral organizations, and they worked relentlessly in the U.N. committees, commissions and agencies to deprive the state of Israel of legitimacy and to legitimize their own struggle and claim to power."

When Kirkpatrick wrote that, 20 years ago, such tactics had already borne considerable fruit. Since then, the process has continued. Thus do we have a U.N. in which democratic Israel is treated as a pariah state, repeatedly condemned, kept off a Security Council that in recent years has included Syria and is being chaired this month by Libya.

Thus do we have a General Assembly dominated by the Organization of the Islamic Conference, overseeing a Human Rights Council that spends most of its time condemning Israel and is now spawning a repeat of its anti-Semitic, anti-democratic 2001 Durban conference on "racism."

What's shifting today is that America, since defying the U.N. in 2003 over Iraq, now looks increasingly inclined to acquiesce to these tactics in the name of "engagement." President Obama, to his credit, recently declined to send delegates to the U.N.'s Durban Review conference this April in Geneva (though his administration has left the door open for further haggling).

But Durban II is just one skirmish in a broad front on which the U.S. and its most basic principles and values are under attack by the U.N. And from the U.N., thanks in great part to America's money, hospitality and trust, America's enemies derive a form of legitimacy and influence they would not otherwise enjoy.

That is the real meaning of d'Escoto's road show and ensuing press conference, framed with the baby-blue regalia of the U.N. draperies, stage and logo, in which he called for "A United States committed to respecting the sovereign equality of all member states." In this formulation, that "respect" for "sovereign equality," would erase vital distinctions between the free and democratic society of America, and the totalitarian, terrorist-wielding strategies and ambitions of a regime such as that of d'Escoto's pals in Tehran. It is not only Israel that today is the target of this campaign to delegitimize; it is the system and sovereignty of America itself.

From the stage of the U.N. briefing room Tuesday, helping himself to a word from Obama's playbook, d'Escoto hailed today's era of increasing American "engagement" as "an opportunity for change. Real change."

He's right. There is a real opportunity here for folks like d'Escoto and his generous hosts in Tehran to rally the mob. We have seen how this works, and it is far from harmless.

Claudia Rosett, a journalist in residence with the Foundation for Defense of Democracies, writes a weekly column on foreign affairs for Forbes. Forbes