WASHINGTON — Officials at the American Israel Public Affairs Committee knew the odds were against them in the fight to block President Obama’s nuclear deal with Iran from surviving a congressional vote. But the influential pro-Israel group threw itself into a nearly $30 million advertising and lobbying effort to kill the accord anyway.

On Thursday, the committee, known as AIPAC, was handed a stinging defeat. After Mr. Obama mustered enough Democratic backing in the Senate to halt a vote on a resolution of disapproval against the deal, a group known for its political clout saw its power and reputation in Washington diminished.

“They failed — they couldn’t even get a vote,” said Clifford Kupchan, an Iran expert and the chairman of the Eurasia Group, a consulting firm, who noted that AIPAC had gone “all in” and tried everything to stop the deal. “It’s among the biggest setbacks for AIPAC in recent memory.”

The loss has raised difficult questions about the future of AIPAC, a group formed in 1951 just a few years after the birth of Israel. AIPAC has long drawn its political potency from its reservoirs of loyalty among members of both parties, but that bipartisan veneer all but vanished in recent weeks as the debate over the Iran deal became increasingly bitter.

Republicans lined up unanimously with AIPAC against the accord, which Mr. Obama had made his top foreign policy priority. The vast majority of Democrats supported it.

“They will be able to recoup, but it is inescapable that there will be stocktaking,” said Dennis B. Ross, a former senior adviser to Mr. Obama who is a distinguished fellow at the Washington Institute for Near East Policy. “And one of the lessons they will have to learn is that you really have to be very careful about the fights you pick that take on what amounts to a purely partisan character, because that bears a cost to you as an organization.”

AIPAC now faces a debate within its ranks about how to respond to the defeat, whether by exacting a political price from lawmakers — all of them Democrats — who defied its wishes and supported the Iran deal, or moving swiftly to mend fences with lawmakers and White House officials angered by the group’s efforts to kill the deal.

“On one hand, they will have a desire to show there are consequences when you go against them,” Mr. Ross said. “On the other hand, they certainly want to maintain a nonpartisan approach, so they will have to think this through.”

In interviews on Thursday, several people close to the organization said the issue was under active discussion. Marshall Wittmann, AIPAC’s spokesman, said the group’s entire attention had been on the vote, “so we have not yet focused at all on the day after, but we are very committed to ensuring that Israel remains strong in the wake of this decision.”

To be sure, the loss was only the latest in a string of hard-fought defeats for AIPAC, which has found itself at odds with presidents of both parties over issues Israel deemed essential to its security. It emerged from all of them with its reputation for lobbying superiority intact and in some cases stronger.

AIPAC feuded with Jimmy Carter in 1978 over his plan to sell F-15 Eagle fighter jets to Saudi Arabia, and three years later battled with Ronald Reagan over Awacs reconnaissance planes for the Saudis. The group lost both times and suffered a similar defeat when George Bush opposed loan guarantees for Israel in 1991.

Stoking opposition to Iran… and to a nuclear deal that even supporters voiced strong reservations with, was in some ways an “organizational imperative” for AIPAC, one that allowed it to underline its mission and mobilize its activists, said Aaron David Miller, a former Middle East negotiator now at the Woodrow Wilson International Center for Scholars. At the same time, Mr. Miller said, the battle took on an striking degree of partisanship.

“That poses a real challenge to an organization that absolutely requires bipartisanship to maintain its resilience and strength,” Mr. Miller added.

Yet AIPAC claimed victory on Thursday even in the face of defeat, issuing a statement asserting that a bipartisan Senate majority had opposed the deal. (The bipartisan majority consisted of all Senate Republicans and four Democrats.) That opposition, the statement said, “sent a strong message to the world that the American people are deeply skeptical about Iran’s willingness to meet its commitments and the long-term viability of this agreement.”

Mr. Wittmann said that AIPAC still believed “very firmly that this was a fight worth fighting,” even as he noted that the outcome was “not what we would have preferred.”

The net effect of the group’s effort, he said, is that the Iran nuclear agreement is “clearly going ahead without the support of a bipartisan majority of Congress or the American people, and that’s significant given that there was a major lobbying campaign by the entire administration.”

Mr. Wittmann said the group was not concerned about losing power or its bipartisan reputation as a result of the battle over the deal, noting the long history of earlier setbacks it sustained without apparent harm to its influence. “Each time, people have said, ‘Well, this is the end of the world as we know it,’ but we know that the U.S.-Israel relationship goes on and has grown ever stronger,” he said.

Jeremy Ben-Ami, the executive director of J Street, a pro-Israel group that lobbied intensively in support of the Iran nuclear deal and spent $3.2 million on pro-deal advertising, said the defeat for AIPAC had shown that the group no longer had a lock on American Jews, and that lawmakers who might once have feared the political consequences of breaking with the group were no longer intimidated.

“The politics on this issue, I think, have changed in a way that they’re not going back, and there’s a recognition of different voices for the American Jewish community that haven’t been heard before,” Mr. Ben-Ami said.

He predicted that after the 2016 elections, lawmakers who backed the deal “will feel like they had the political support that they needed from the Jewish community to win re-election.”

Opponents of the accord were not so sure.

“I think you may see donors withholding or not wanting to write a check to people because they feel betrayed, and there’s going to have to be some accountability here,” said Josh Block, the president of The Israel Project, a pro-Israel public relations group. “There’s no question in my mind that people’s votes on the Iran deal are going to be an issue in the next election cycle, and the one after that, and the one after that, and they’ll be held accountable.”

(Source: New York Times)