It would be a catastrophe for American influence in the world if Congress killed the Iranian nuclear deal.

Perhaps because the stakes are so high, the debate has become poisonous. Critics are (ludicrously) accusing President Obama of appealing to anti-Semitic tropes. And Obama (petulantly) suggested that some opponents were “alarmist,” “ignorant,” “not being straight” and “making common cause” with Iranians who chant “Death to America.”

Obama’s rhetoric was counterproductive. As former Senator Kay Bailey Hutchison, a Texas Republican, told me, “At this point, the president has made it impossible for a Republican to vote for it.” Constituent calls to congressional offices are overwhelmingly against the deal, and with Senator Chuck Schumer defying the White House by opposing it, the opposition is more bipartisan than the support is. That’s tragic, for killing the deal would infuriate many allies, isolate America rather than Iran and ultimately increase the risk of ayatollahs with nuclear weapons.

I’ve already explained why I’m strongly in favor of the deal, and I urge President Obama to start over with his sales job and focus on three points.

First: Sure, the deal is imperfect, but it’s the best way to achieve a goal we all share passionately — preventing Iran from developing nuclear weapons.

The great majority of arms experts support the deal, some enthusiastically, some grudgingly. They recognize shortcomings, but on balance, as 29 of America’s leading nuclear scientists and arms experts wrote in an open letter last week, it has “much more stringent constraints than any previously negotiated nonproliferation framework.”

Likewise, three dozen retired American generals and admirals released a joint letter declaring the deal “the most effective means currently available to prevent Iran from obtaining nuclear weapons.”

Iran would go from maybe a few months from a bomb to a year away. The agreement doesn’t solve the underlying problem, but it may buy us 15 years.

Yes, it would be nice if Iran gave up all its enriched uranium. But isn’t it better that it give up 98 percent of its stockpile than that it give up none?

Everyone knows Prime Minister Benjamin Netanyahu of Israel opposes the deal, but not everyone realizes other Israelis with far more security expertise support it. Ami Ayalon, former head of Israel’s Shin Bet security service, describes it as “the best possible alternative.” And Efraim Halevy, former head of the Mossad, says, “What is the point of canceling an agreement that distances Iran from the bomb?”

Second, it’s true that Iran may try to cheat, but it’s easier to catch and stop the cheating with the deal than without.

Critics sometimes note that President Bill Clinton reached an agreement on nuclear weapons with North Korea in 1994, only to see North Korea cheat. The lesson they draw is that it’s pointless to negotiate with untrustworthy rogue regimes.

I’ve covered North Korea since I was a young reporter in Asia in the 1980s, and the lesson is actually more like the opposite.

That 1994 agreement was indeed flawed, and North Korea violated it. But even so, in the eight years the agreement was in place, North Korea made zero nuclear weapons, according to American intelligence estimates. After the deal collapsed in 2002, the Bush administration turned to a policy of confrontation, and North Korea then made perhaps nine nuclear weapons.

Third, if all goes south, or if Iran is stalling us and after 15 years races to a weapon, we retain the option of a military strike.

I asked David Petraeus, retired four-star general and former head of the C.I.A., about that. “I strongly believe,” he told me, “that there will continue to be a viable military option should Iran seek to break out and construct a nuclear device after the expiration of many of the elements of the inspections regime at the 15-year mark of the agreement.”

To me, this deal is ugly and flawed — and infinitely better than the alternatives. The criticisms of the deal strike me as reasonable, but the alternatives that the critics propose seem unreasonable and incoherent.

So President Obama should hit the restart button. He should acknowledge that the deal has shortcomings but also emphasize that it must be judged not by a referendum on its terms but rather as a choice: deal or no deal.

He can also take steps to reassure doubters. We could boost funding for the International Atomic Energy Agency to make oversight more effective. We could do more to speak up for human rights in Iran and to counter Iranian meddling in the region, especially in Syria.

Gen. Brent Scowcroft, the patriarch of Republican security experts, tells me that he supports the Iran deal in part because it exemplifies American leadership on a crucial global issue. I agree, and for Congress to kill it will not just set back American leadership, it will also increase the odds that Iran gets the bomb.