After his speech on the Iran deal, Obama acknowledged that the vote could be close. “Everything in this Congress squeaks by,” he said. “If I presented a cure for cancer, getting legislation passed to move that forward would be a nail-biter.” PHOTOGRAPH BY PETE MAROVICH / POOL / GETTY

With the most important foreign-policy initiative of his Presidency at stake, President Obama has gone on the offensive to salvage his controversial Iran nuclear deal, amid a blitz of television ads and opposition, both at home and abroad. On Wednesday, Obama chose American University—the campus where John F. Kennedy outlined his vision for peace, in 1963, during the early age of nuclear threats—to make his strongest pitch to date. He framed the deal as the latest step in a half century of American policy to avert nuclear confrontation, invoking Kennedy’s diplomacy during the Cuban missile crisis and the arms negotiations with the Soviet Union launched by Ronald Reagan. Under both Democratic and Republican Presidents, he said, the historic Non-Proliferation Treaty and the SALT and START treaties introduced arms control.

“The world avoided nuclear catastrophe, and we created the time and the space to win the Cold War without firing a shot at the Soviets,” he said. The deal with Iran, reached after twenty months of negotiations, “builds on this tradition of strong, principled policy diplomacy.” Obama mentioned that he had been forced to make a lot of tough calls as President. “But whether or not this deal is good for American security is not one of those calls,” he said. “It’s not even close.”

The decision facing Congress, which must act on a Republican-introduced resolution of disapproval no later than September 17th, is the most important since its vote on the 2003 invasion of Iraq, Obama said. Without naming George W. Bush, the President contrasted his own use of diplomacy with Bush’s rush to war, noting that the Iraq adventure cost nearly a trillion dollars, took thousands of American lives, and left Iraq ripped apart by sectarian violence.

Obama condemned the “knee-jerk partisanship” in Washington, which “renders every decision made to be a disaster, a surrender. ‘You’re aiding terrorists! You’re damaging freedom!’ ” He also went after lobbyists and pundits who had suddenly become “arm-chair nuclear scientists.”

After the speech, in an afternoon session with ten journalists, Obama acknowledged that the vote could be close. “Everything in this Congress squeaks by,” he said. “If I presented a cure for cancer, getting legislation passed to move that forward would be a nail-biter.”

The California Republican Ed Royce, who is Chairman of the House Committee on Foreign Affairs, introduced language for the resolution of disapproval Tuesday. “The agreement gives Iran permanent sanctions relief, but in exchange only temporarily restrains Iran’s nuclear program,” Royce said. “If this agreement goes through, Iran gets a cash bonanza, a boost to its international standing, and a lighted path toward nuclear weapons.” The United States will be less able to challenge Iran “across the board,” he said. “As Iran grows stronger, we will be weaker to respond.”

Obama is spending a significant amount of his time trying to rally support, working members of Congress and American Jewish groups, deploying staff to make pitches outside Washington, and dispatching his Secretary of State to the Middle East this week to calm nerves there about the future.

American Jews have been central to the debate, and to the large media campaigns, both for and against the deal. On its Web site and in television ads, the American Israel Public Affairs Committee (AIPAC) is lobbying hard against the agreement. The more liberal JStreet has supported it. In a setback for the White House, three Jewish Democrats—Representatives Nita Lowey and Steve Israel, of New York, and Ted Deutch, of Florida—announced Tuesday that they will vote against the deal. Lowey is the top Democrat on the House Appropriations Committee. Deutch is the senior Democrat on the House Middle East subcommittee.

Obama’s main international adversary on the agreement is Benjamin Netanyahu, the Prime Minister of Israel, America’s closest ally in the Middle East. In a Webcast address to American Jewish organizations, on Tuesday, Netanyahu warned that the deal would give Iran two paths to a bomb: either by keeping to the terms of the deal over its limited time period—after which it will be a “threshold nuclear-weapons power”—or by violating it outright. “As a result of this deal, there will be more terrorism, there will be more attacks, and more people will die,” Netanyahu warned.

Obama is clearly exasperated with Netanyahu’s campaign, even as he acknowledges Israel’s legitimate alarm over Iran’s anti-Semitism and its repeated denial of the Holocaust. “This is the strongest non-proliferation agreement ever negotiated,” he said. “And because this is such a strong deal, every nation in the world that has commented publicly, with the exception of the Israeli government, has expressed support.” The United Nations Security Council has also given it unanimous backing.

Obama ticked through the main arguments against the deal. To cheat, Iran would have to build a massive covert operation and many covert facilities. “No nation in history has been able to pull off such subterfuge when subjected to such rigorous inspections,” he said. The prohibition against making a bomb is permanent—not limited to any of the ten-to-twenty-five-year time frames for various aspects of a program. U.N. inspectors will be allowed daily access to nuclear sites, as well as the right to look at suspicious undeclared sites. “This access can be with as little as twenty-four hours’ notice,” Obama said. “And while the process for resolving a dispute about access can take up to twenty-four days, once we’ve identified a site that raises suspicion, we will be watching it continuously until inspectors get in.”

Obama acknowledged that some of the sanctions relief—which the United States now says amounts to fifty-six billion dollars, rather than the previously estimated hundred billion—could end up in the hands of the Revolutionary Guards. At the same time, Iran now has more than a half trillion dollars in “urgent requirements” to bail out its troubled economy, Obama said. “Iran’s leaders have raised the expectations of their people that sanctions relief will improve their lives. Even a repressive regime like Iran’s cannot completely ignore those expectations.” In short, “there’s no scenario where sanctions relief turns Iran into the region’s dominating power.” He noted that the six Gulf sheikhdoms have a combined budget eight times larger than Iran’s defense spending. “If we’re serious about confronting Iran’s destabilizing activities, it is hard to imagine a worse approach than blocking this deal.” He argued that proposals to walk away from the deal and either maintain sanctions or try to get better terms were “selling a fantasy.”

In an appeal to Americans to contact their representatives in Congress during the final weeks of debate, Obama again invoked Kennedy, who said, “The pursuit of peace is not as dramatic as the pursuit of war.”

As Washington has struggled over a decision, European ministers have been scrambling to Tehran since the deal was announced, on July 14th. The French foreign minister, Laurent Fabius, who sometimes took tougher positions than the Americans during the negotiations, was in Tehran within days—hand-carrying an invitation for President Hassan Rouhani to visit Paris this fall. “Things will, we hope, be able to change,” he said, during a press conference. Italy soon followed suit, and Germany dispatched its economics minister.

Meanwhile, people in Tehran have been captivated by the debate in Washington. Iranian television broadcast some of the hearings live last week, with subtitles. The Iranians know that their future will also be decided by what happens on Capitol Hill.