WASHINGTON -- The Russian-American deal to destroy Syria's chemical weapons arsenal gives President Obama some breathing space after a politically damaging few weeks. But the list of things that could still go wrong is extensive and daunting.
The two sides could deadlock over the text of a United Nations Security Council resolution codifying the agreement. Syria could insist on deal-breaking conditions or fail to turn over a complete accounting of its weapons within a week, as mandated. International inspectors could be obstructed on the ground or chemical stocks could be hidden from them.
Given all that, Mr. Obama has decided to leave American destroyers in the eastern Mediterranean Sea to preserve the possibility of a military strike. But as the president and his team look ahead several steps, they are struggling to come up with a viable Plan B in case the agreement does not work, finding that they have few if any appealing options.
"Ronald Reagan says, 'trust but verify,' and I think that's always been the experience of U.S. presidents when we're interacting with, first, Soviet leaders and, now, Russian leaders," Mr. Obama said in an interview on ABC's "This Week" on Sunday. But he offered little insight into what he would do if he could not verify Syria's compliance with the Russian-brokered deal to turn its chemical weapons over to international inspectors for destruction.
As he waits to see if the diplomacy succeeds, Mr. Obama also faces the issue of whether to increase aid to the rebels fighting to topple the government of President Bashar al-Assad. Senators Robert Menendez of New Jersey, the Democratic chairman of the Foreign Relations Committee, and John McCain of Arizona, the Republican champion of the Syrian opposition, urged him to during interviews on NBC's "Meet the Press" on Sunday.
Doing so, however, could upend the chemical weapons deal. Mr. Obama has said his now-aborted military strike was aimed only at punishing Mr. Assad for an Aug. 21 chemical attack that the United States says killed more than 1,400 people and deterring future attacks -- not at changing the equation of a civil war that has killed more than 120,000 people. But the president also has said Mr. Assad should step down. Increasing aid to make that happen, even on a separate yet parallel track, could provoke Mr. Assad into refusing to hand over his chemical stockpiles.
The situation is reminiscent of the years-long international oversight of Iraq after the Gulf War of 1991, when Saddam Hussein often seemed to play cat-and-mouse games with United Nations inspectors, and the United States had to decide when it amounted to punishable defiance. In late 1998, President Bill Clinton concluded that Mr. Hussein was violating his agreement to destroy his unconventional weapons and ordered several days of airstrikes.
"The toughest thing going forward is what amounts to a breach of deal," said Representative Adam Smith of Washington State, the top Democrat on the House Armed Services Committee. "If Syria is two days late giving us all the information on the weapons or we don't destroy them as quickly as we want to -- that's what the president has to deal with. It's not going to be a clear line. There's a variety of ways for them to slow-walk this."
Russia, which advanced its diplomatic initiative to prevent an attack on Syria, has made clear it will use its veto in the Security Council to block any authorization of military action to enforce the deal. So if it falls apart, Mr. Obama again will face the prospect of ordering a strike without international backing.
The more pressing question would be whether to go back to Congress. Although Mr. Obama claimed the power to attack Syria on his own, just as Mr. Clinton did with Iraq, he sought authorization from lawmakers anyway on the theory that a unified front would be stronger. Instead, he found that the more he argued for a strike, the more polls showed him losing public support and the more certain defeat on Capitol Hill became.
For the moment, aides say it is still Mr. Obama's position to have Congress sign off on any military operation if the Russian-American disarmament agreement collapses. But senior lawmakers have told the White House that it cannot win such a vote, and some outside advisers said Mr. Obama should skip Congress if the Russian gambit fails.
"Plan B needs to be carrying out strikes" and "probably avoiding a vote on the Hill," said Dennis B. Ross, a Middle East expert who has advised Mr. Obama. "To have the diplomatic initiative fail and not carry out strikes would certainly make it hard to convince anyone that our words mean anything."
Colin Kahl, a former Pentagon official under Mr. Obama, said a "credible threat of military force needs to be left on the table" and suggested the president might seek a conditional measure authorizing action if Syria reneges. "If there was widespread support for that sort of contingent authorization, I think they would go ahead and move forward with it," Mr. Kahl said. "But otherwise, I think there's a possibility that they wouldn't" go back to Congress.
Yet having asked Congress once to weigh in, Mr. Obama would be hard pressed to explain why he would now bypass it. The criteria he set for requesting a Congressional vote -- a situation that was not an imminent or a direct threat to the United States -- would still apply. Some allies believe that could leave him more politically isolated than if he had never asked in the first place.
Some Democrats said Mr. Obama might be bolstered in Congress if the Russian initiative did not work. "I would say that actually strengthens the president's hand coming back to Congress because he's able to say, 'All right, I walked the extra mile you asked me to even though it was a little embarrassing. I did what you asked me to do,' " said Representative Gerald E. Connolly, a Virginia Democrat.
But lawmakers and aides in both parties said Mr. Obama has so little support for a strike that it might not make a difference. They said they saw no chance that Mr. Obama would prevail in the House, and he might even lose in the Senate, where Democrats have a majority. Yet it would be hard to "un-ring the bell," as one Congressional aide put it, and act without Congress, having asked once.
Most lawmakers on both sides of the aisle just want the issue to go away. Indeed, the White House recommended to lawmakers that they move on to other subjects. The White House itself pivoted its public message back to economic issues on Sunday. Mr. Obama and Congress face critical deadlines in the next few weeks to keep the government open and avert a default.
The prolonged process of finalizing a disarmament plan and putting it into effect over the course of a year would take Syria off the front burner for a while and could give Mr. Obama an opportunity to avoid action altogether. Senior administration officials made the case last week that the process itself serves as a deterrent because Mr. Assad presumably would not use his chemical weapons in the interim.
"I just don't know what the answer is," said Representative Peter T. King, a Republican from New York who has argued that Mr. Obama should not ask Congress for permission to strike. "I've never seen a policy going in so many different directions." He added: "In many ways it's like amateur night. This just seems to be ad hoc."
This article originally appeared in The New York Times.