The “Death to America!” chant was a recurring point of conflict in both the Senate and the House committee hearings on the nuclear deal with Iran. PHOTOGRAPH BY FATEMEH BAHRAMI / ANADOLU AGENCY / GETTY

The fate of the Iran nuclear deal may be determined less by details in a weighty document, drawn up by the world’s six major powers, than by a three-word incantation that persists thirty-six years after Iran’s revolution. “Death to America!” hangs heavy, and maybe decisively, over the debate in Washington.

“Is it the policy of the Ayatollah, if you can answer for him, that Iran wants to destroy the United States?” the Texas Republican Ted Poe, of the House Foreign Relations Committee, asked Secretary of State John Kerry, on Tuesday.

“I don’t believe they’ve said that,” Kerry replied. “I think they’ve said ‘Death to America!’ in their chants.”

“Well, I kind of take that to mean that they want us dead,” Poe countered.

“I think they have a policy of opposition to us and a great enmity, but I have no specific knowledge of a plan by Iran to actually destroy us,” Kerry said. “I do know that the rhetoric is—is beyond objectionable.”

The chant was a recurring point of conflict in both the Senate and the House committee hearings this week. “You would think that after an agreement was signed with us there might be a modicum of good will that perhaps they would keep quiet for a week or two, or a month. But it went back to business as usual,” the New York Democrat Eliot Engel told Kerry. “How can we trust Iran when this type of thing happens?”

Over the decades, I’ve heard “Death to America!” shouted routinely at Friday prayers, and at commemorations of the U.S. Embassy takeover and other demonstrations. The regime refuses to shelve the slogan. These days, however, students are often bussed in on anniversaries as crowd-filler; the perk is a day off from school. They chant when prompted. The enthusiasm is a bit like the anti-American graffiti on public walls—it hasn’t been painted over, but it’s fading.

During the final weeks of diplomacy between American and Iranian diplomats, I talked to Iranians in Tehran from across the political spectrum about “Death to America!” I pointed out that, throughout the decades of tension, no American has been recorded going into a church and shouting “Death to Iran!” Some Iranians downplayed the revolutionary mantra’s importance; others insisted it still has strong symbolic merit. But all of them—particularly senior Iranian officials educated in the United States—seemed befuddled about why it would ever impact the fate of the nuclear deal.

The gap in perception may be the deal’s greatest vulnerability. Mohammad Nahavandian, an economist, is chief of staff for President Hassan Rouhani. He spent eight years living just a few blocks from the White House while working on his doctorate at George Washington University. He had a green card for residence in the United States but, he told me, gave it up to take his current position—and after it became an issue in Iran’s parliament.

“If you go and ask anyone who uses that slogan . . . what he is against, it is interference in Iran’s policies by overthrowing a nationally elected prime minister at the time of Mossadegh.” He meant the 1953 C.IA.-sponsored coup against Iran’s democratically elected Prime Minister, Mohammad Mossadegh. “For them, what they are against is the kind of government who shoots an airplane full of innocent passengers,” he said, referring to the 1988 downing of an Iranian airliner by an American naval vessel. “For them, it’s not the people of America, per se. For them, they are opposed to that sort of policy, that sort of attitude, that sort of arrogance. It’s not a nation. It’s a system of behavior.”

Amir Zamaninia, who did graduate work at Chico State, in California, is now Iran’s deputy Oil Minister for International and Commercial Affairs. His son, he told me, is studying philosophy at Rutgers. A former diplomat, Zamaninia is now planning projects totalling two hundred billion dollars to develop Iran’s oil and gas industries over the next six years. He’s hoping for foreign investment if sanctions are limited. “What Iranians want next is to persuade the public in the United States not to think that we have nothing to do but be on the streets shouting ‘Death to America!’ every day,” he said. “We have our business, our own entertainment, and our own life to live. Saying ‘Death to America!’ has been a permanent fixture of the revolution that we don’t listen to anymore. It comes out as a matter of routine.”

Hossein Sheikholeslam was one of the Berkeley mafia, a group of young Iranians educated in northern California, several at Berkeley, who returned to Tehran after the 1979 revolution to play prominent roles in the new government. After the U.S. Embassy seizure, he was brought in from the Ministry of Islamic Guidance because of his English. The American hostages nicknamed him “Gap Tooth,” for an obvious reason. (He had no gap when I met him in May. “It’s artificial,” he said, tapping his front teeth. He’d had them filled.) Sheikholeslam also helped assemble the C.I.A. documents hurriedly shredded during the takeover. He went on to become deputy foreign minister, Iran’s ambassador to Syria, and is now foreign-policy adviser to Iran’s parliament.

“The United States is still oppressing us—at least, change your policy toward us,” he said, in the course of a chicken-and-egg discussion. “We can’t have your embassy here when people still shout ‘Death to America!’ And the Supreme Leader can’t say, ‘Stop shouting this phrase,’ because he is the essence of the Iranian people.”

Kayhan Barzegar was at Harvard’s Belfer Center for Science and International Affairs between 2007 and 2011. He is now director of the Institute for Middle East Strategic Studies in Tehran. “We are seeing America in a new way, in a good way, but not in a sympathetic way,” he said. “We are seeing that America is accepting Iran’s reality as a state with its own ambitions, its own independent way of doing politics, in domestic or foreign policy. We don’t need to be recognized by America. We don’t need to make the case to be recognized by America, because Iran is a reality.” But, he cautioned, “You should not expect politics to be exercised in a very polite way. Politics goes that way because of the sense of fear.”

Nasser Hadian got his doctorate at the University of Tennessee and taught at Columbia. He is now a Tehran University political scientist and influential voice in policy circles. His daughter is in graduate school at Tulane. “Saying ‘Death to America’ is meaningless,” he told me. “It’s actually not acceptable in our culture, because they’re saying death to a whole people. It’s said by only twenty per cent of the population. And only a teeny per cent of that twenty per cent believes in it. They think America crystallizes and stands for all bad things in the world—the same way some Americans think about Iran. America has killed more Iranians than Iranians have killed Americans. The U.S. supported Saddam Hussein during his war with Iran, when hundreds of thousands died.”

He went on, “For others, it’s part of a religious ritual. But the élite who use it exploit the term for political reasons. Poll after poll shows that Iranians are greater supporters of America than any other Muslim country in the region.

“So whom does America want to rely on to judge public opinion?” Hadian asked. “The twenty per cent who do shout ‘Death to America!’ or the eighty per cent who don’t?”