If the U.S. Congress votes down the nuclear deal with Iran, President Barack Obama could rapidly find himself facing many negative reverberations, including a painful predicament with China, current and former U.S. officials said on Friday.
China, one of six world powers that negotiated with Tehran, has reduced the amount of Iranian oil it buys, as demanded by a U.S. sanctions law meant to pressure Iran to accept a diplomatic resolution of the nuclear stand-off.
If Congress scuttles the July 14 nuclear agreement, energy-hungry Beijing is likely to conclude diplomacy has failed, break free of sanctions restraints and increase Iranian oil imports, the officials said.
Obama would have to decide whether to sanction China and add new troubles to bilateral relations - or let the painstakingly built architecture of restrictions on Iran unravel.
"You will rapidly find that we will have to make sanctions decisions that are not very attractive," said Richard Nephew, until recently a top State Department and White House sanctions official.
The China example is just one of numerous consequences expected if Congress were to block the Vienna agreement, which offers Iran relief from sanctions in return for limits on its nuclear work, U.S. officials and European diplomats predicted.
They include a possible trans-Atlantic schism over the issue; Iran's nullification of the deal and its rapid resumption of large-scale nuclear enrichment; and even U.S. court battles over the sanctions.
Obama's White House is fighting for the agreement - which would be a legacy achievement for the president - and has plenty of motivation to cast the alternatives as dire.
The president has depicted the choice as "between diplomacy or some form of war" with Iran, but European allies and many outside analysts agree that scuttling the deal would be costly.
"That would be a big, big, big blow to the United States in the world. It would also be bad for the whole Middle East, bad for Israel," former European Union foreign policy chief Javier Solana, who helped launch the first nuclear talks with Iran in 2004, told Reuters.
FACING A STIFF CHALLENGE
Supporters of the deal, which is being scrutinized in Congress, suffered a setback on Thursday when a top senator from Obama's Democratic party, Chuck Schumer of New York, announced his opposition.
Opponents still face a stiff challenge in defeating the agreement after a review process that ends in September.
If the Senate and House pass resolutions of disapproval, Obama has said he would veto them and Democrats in Congress said on Friday they were confident they had the votes to uphold the veto.
But should opponents prevail, Obama would likely be unable to implement the nuclear deal on his own by defying Congress and unilaterally offering sanctions relief to Iran, current and former U.S. officials said.
If Congress passes a resolution of disapproval and overrides a veto, under a law passed in May, Obama's ability to waive any sanctions passed by Congress - the vast majority of U.S. sanctions - would be eliminated.
Obama might try to revoke or modify his own presidential executive orders that imposed some of the sanctions.
But "95 percent of the E.O.s (executive orders) are basically already part of U.S. law" mandated by Congress, said Nephew, now at Columbia University. "The rest is kind of small fry."
Without promised U.S. sanctions relief, many observers say, Iran would likely not implement its end of the deal. It might even ramp up enrichment of uranium that could eventually be used for a nuclear weapon.
Under another scenario that senior U.S. officials have studied, Iran would instead begin complying with the accord even if Congress voted it down. Many countries might respond by ceasing to comply with sanctions against Iran, creating a rift with Washington.
Not everyone agrees that a U.S. congressional "no" vote would bring catastrophe.
Robert Satloff, executive director of the Washington Institute for Near East Policy, said that U.S. and European sanctions relief for Iran does not kick in until mid-2016, after Tehran has begun implementing agreed nuclear steps.
Iran is likely to comply, in any event, to get promised international sanctions relief, Satloff said. The view "that everything collapses because of a disapproval" by Congress "doesn't hold water," he said.
