The nuclear agreement with Iran is supported by almost every nation in the world. It has the backing of nearly the entire American security establishment, current and retired. It enjoys the overwhelming support of nuclear scientists and policy experts. There is no credible alternative.
And yet, with almost a month to go before the vote, lobbying against the deal is intense. No Republican senator supports the agreement. Two prominent Democratic senators, Charles Schumer and Robert Menendez, have denounced it.
Here is how rejection would play out.
First, our allies would desert us. This is not just an agreement struck between the United States and Iran. It is a deal negotiated over two years by the world powers. America led the way, but Russia, China, the conservative governments of Britain, France and Germany, and the entire European Union were equal partners. Everyone had to agree on every term or there would have been no deal.
Opponents spin fanciful notions of a "better deal" with tougher terms, bigger sticks. This is nonsense. Our European partners have already told us that it is this option or nothing. If Congress blocks the deal, no nation, least of all Iran, will believe that the United States is capable of making and keeping a new agreement. U.S. credibility would collapse faster than the Chinese stock market.
The sanctions regime would then unravel. The U.S. persuaded most of the world to curtail their trade and financing with Iran because we presented a feasible path to a diplomatic solution. Take away diplomacy and the sanctions cannot hold. Any new ones passed by Congress would be feckless.
"The idea that you can put sanctions on the whole world, including our allies, is not promising," former head of the Federal Reserve Paul Volcker said last week. Expecting the world to go along with new sanctions "when the U.S. is the one that backs out is not a strong negotiating position, to say the least." Even our closest allies would steadily resume oil trade, investments and banking with Iran.
Hard-liners in Iran would also reassert their dominance. If you liked the Iranian government led by Mahmoud Ahmadinejad, you are going to love the new one that would sweep into office once the centrist government of Hassan Rouhani is thrown out in disgrace. Iran's supreme leader, Ayatollah Ali Khamenei, would announce that he was right not to trust the Americans. The hopes of the young, educated population for a new chance at reform would be crushed.
These conditions almost certainly would lead to a renewed Iranian nuclear program. For 10 years, as sanctions and the threat of military force grew, so did the number of Iranian centrifuges. It was only diplomacy that halted and then rolled back the program. With diplomacy over, sanctions withering and the hard-liners in ascendancy, Iran's nuclear program would come back with a vengeance. In short order, the Iranians could have tens of thousands of centrifuges enriching tons of uranium. They would be able to make enough for multiple bombs within days, not the full year the deal provides before they could make enough material for just one bomb.
Could Israel live with that threshold capability? Its political leaders have repeatedly said they couldn't and threatened attacks if Iran gets this close to a bomb. U.S. hawks are eager to back them. Sen. Tom Cotton (R-Ark.) says U.S. military strikes would be quick, cheap and effective.
U.S. military leaders are more sober about how difficult war would be. Draft U.S. plans call for weeks of airstrikes. Thousands of Iranians would die. Retaliation would be certain, including elite Quds Force attacks on U.S. and Israeli targets around the world. Iranian militias and the Revolutionary Guard would strike U.S. forces in the region. Iran would close the Strait of Hormuz, through which one-fifth of the world's oil flows.
And war would not stop an Iranian bomb; it would accelerate it. U.S. military leaders estimate bombing would set back the Iranian program by only one to three years. Tehran would put the pedal to the metal. There would be no debate on whether to build a bomb. The population would rally around an otherwise unpopular regime, and the people would see a nuclear weapon as their only protection from a belligerent United States and Israel.
All of this is preventable. The deal in hand would stop an Iranian bomb and prevent a potential war. Congress would be foolish to reject this historic opportunity.
Joseph Cirincione is president of Ploughshares Fund, a global security foundation.