WASHINGTON — Republican efforts to stop the nuclear agreement with Iran ended in failure Thursday, thwarted by unflinching Democratic support for President Obama’s landmark accord and familiar GOP infighting.

With no clear strategy remaining to prevent the internationally backed deal, Republican leaders in Congress were left conducting largely symbolic votes that will register lawmakers’ rejection of the deal but do nothing to upend it.

In the Senate, Republicans were met with a Democratic filibuster that blocked a resolution of disapproval, preventing it from being sent to the president’s desk and depriving the GOP of a hoped-for veto showdown.

On a vote of 58 to 42, the Democratic and independent senators backing the agreement stopped Republicans from reaching the 60-vote threshold needed to advance the disapproval measure toward passage.

Four Democrats who opposed the deal joined all 54 Republicans, but they fell short. Senate Majority Leader Mitch McConnell, R-Ky., vowed to try again, pressuring senators supporting the measure to relent.

Maine’s Sen. Angus King, an independent, voted with the majority, while Sen. Susan Collins, a Republican, voted against it.

Collins, who had withheld her views on the deal until recently, said:

“The agreement is fundamentally flawed because it leaves Iran as capable of building a nuclear weapon at the expiration of the agreement as it is today.”

King said it was a difficult decision to make, but added that “If you analyze the alternatives and weigh the risks, I believe that the risks of not going forward with this agreement are significantly greater than the risks of giving diplomacy a chance.”

Republican leaders, meanwhile, said the were not ready to give in.

“No amount of saying this is over makes it over,” McConnell said after the vote, adding that if Democrats were so proud of the Iran deal, they should embrace the outcome. “Break out the champagne. Celebrate. Take credit for it. You own it.” He set up a vote next week to “move past this procedural snag.”

Obama praised the Senate for taking “an historic step forward” that will enable the U.S. to continue working with its partners to “prevent Iran from obtaining a nuclear weapon.”

“Today, I am heartened that so many senators judged this deal on the merits, and am gratified by the strong support of lawmakers and citizens alike,” the president said. “Going forward, we will turn to the critical work of implementing and verifying this deal so that Iran cannot pursue a nuclear weapon, while pursuing a foreign policy that leaves our country – and the world – a safer place.”

A disapproval resolution also failed to come to a vote in the House, despite that chamber’s larger Republican majority and different rules that made passage once appear assured.

Instead, internal party infighting forced a last-minute strategy shift Wednesday and the House began voting Thursday on other measures designed to put Republicans on record against the deal. None are likely to become law. The result over the next several days will be a slow-motion end to a debate that once gave Republicans an opportunity to challenge the White House on foreign policy but has now delivered the president a legacy-building achievement.

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