Ordinarily, when Washington’s most powerful pro-Israel lobby asks senators to do something, lawmakers of both parties are happy to oblige. Not just some of them. All of them. On crucial Capitol Hill votes, measures favored by the American Israel Public Affairs Committee, or AIPAC, often pass unopposed.

Last week was different. Very, very different. First, AIPAC was forced, in the wake of Democratic opposition, to retreat for the moment on the Iran sanctions bill the group had been pushing for months. Then, nearly every Republican in the Senate ignored AIPAC’s call for a retreat on the bill, and decided to keep on pushing for a vote on it, anyway.

Somehow, on the issue arguably of most importance to both the Israeli government and America’s pro-Israel community—Iran and its nuclear ambitions—AIPAC didn’t merely fail to deliver. It alienated its most ardent supporters, and helped turn what was a bipartisan effort to keep Iran in check into just another political squabble. The lobby that everybody in Washington publicly backs somehow managed to piss off just about everyone.

Even the Israeli government isn’t happy with AIPAC’s handling of the sanctions bill. Sen. Bob Corker, the ranking member of the Senate Foreign Relations Committee, said he had a “very direct conversation” with Ron Dermer, Israel’s ambassador to the United States, on the sanctions bill early last month. “AIPAC and Israel are in different places on this issue,” Corker said of his conversation with Dermer, who he said supported the sanctions bill now and not at a later date.

On Feb. 3, AIPAC senior members (known inside the organization as “key contacts”) began reaching out to Republican senators to say that now was not the time to vote on an Iran sanctions bill opposed fiercely by the White House, according to four Senate sources who spoke to The Daily Beast on condition of anonymity. Until then, AIPAC was willing to endure open criticism from the White House, which had described the sanctions push as a rush to war. And why not? With 59 co-sponsors, the bill seemed almost guaranteed to pass.

Among the lawmakers reached were a handful of Republican senators, including Senate Minority Leader Mitch McConnell; Sen. Mark Kirk (the Republican co-sponsor of the bill AIPAC had been pushing to support until then), and Sen. Lindsey Graham, another stalwart ally of Israel.

AIPAC has many ways of communicating with Congress, but the “key contacts” are particularly important. They are AIPAC members that have a personal relationship with a given senator or congressman and are usually either a fundraiser, big donor, or a personal friend, such as a former college roommate, according to a former senior lobbyist for the group. Former AIPAC legislative liaison Ralph Nurnberger defined the key contacts as “someone who has enough of a personal relationship that the elected official would return a phone call within a day.”

Because of these personal relationships, the lobby can often be very effective. Unlike a professional insider in Washington, the key contact has a history with the member of Congress and is already considered an important political ally.

This is one reason why it was so unusual that the vast majority of Republicans on Wednesday evening told Harry Reid they were not going along with AIPAC. According to Senate staffers, the phone calls did not go well. “AIPAC is close to Schumer and Reid, who told them to pull back on the sanctions bill,” one GOP Senate staffer told The Daily Beast. “Republicans responded with a big middle finger.”

The extension of that middle finger began Tuesday afternoon at a weekly lunch for Republican senators. Kirk brought with him a draft of the letter to Reid and made the case to his colleagues to sign it, according to the staff members. A little more than a day later, he had the signatures of 42 out of 45 Republican senators on the letter.

Republicans and Democrats these days bicker all the time. But when it comes to Iran sanctions and pro-Israel legislation in general, the two parties are almost always on the same page. In 2010, the Comprehensive Iran Sanctions, Accountability, and Divestment Act, which first imposed a secondary boycott on Iran’s oil sector, passed the Senate 99 to 0. In 2011, a Kirk-Menendez amendment to blacklist Iran’s central bank from the global financial sector passed the Senate 100 to 0. In 2012, another Kirk-Menendez amendment passed the Senate 94 to 0. And last summer a resolution saying the United States would support Israel if it attacked Iran passed 99 to 0.

Menendez—Kirk’s co-sponsor on the Iran sanctions bill—himself was caught off guard, according to Senate staffers. In his floor speech Thursday, Menendez added a line at the last minute that referenced the Republican effort to continue to push for a vote, saying, “I hope that we will not find ourselves in a partisan process trying to force a vote on this national security matter before its appropriate time.”

After the speech, AIPAC released a statement that said the group agreed with Menendez “that stopping the Iranian nuclear program should rest on bipartisan support and that there should not be a vote at this time on the measure.

That AIPAC press release prompted a rare rebuke from one of the group’s biggest allies on the political right. William Kristol issued a statement from his organization, the Emergency Committee for Israel—a group that has also fought for the Kirk-Menendez bill—warning, “It would be terrible if history’s judgment on the pro-Israel community was that it made a fetish of bipartisanship—and got a nuclear Iran.”

From the perspective of Republican supporters of Israel, AIPAC’s emphasis on bipartisanship in the Obama era has too often meant accommodating a president who has openly clashed with Israel’s prime minister, Benjamin Netanyahu, on some of the most important issues. While Obama has in some cases gone way beyond his predecessors in supporting Israel—such as his funding the development of a rocket defense shield known as Iron Dome—the president has also fought publicly with Netanyahu on the construction of settlements and more recently on whether Iran would be able to keep a nuclear enrichment program in a final deal with world powers.

This has created a dissonance at times between the Israeli government and the organization that lobbies to strengthen the U.S.-Israel relationship. Netanyahu’s first reaction to the interim deal in November after being briefed by Secretary of State John Kerry, for example, was to call it the “deal of the century" for Iran. By contrast, AIPAC took a more muted tone, saying it had a “difference of strategy” with the Obama White House.

AIPAC’s muted tone on the Iran talks opposed by Israel’s government led the group to focus on how to allow Democrats to support a sanctions bill opposed by the leader of their party. On a Dec. 18 conference call to pro-Israel activists and lobbyists, AIPAC Executive Director Howard Kohr told his ground troops to focus on how AIPAC had an “honest policy disagreement not a personality disagreement with Obama,” according to a recording of the call played for The Daily Beast.

In making the case for the Kirk-Menendez sanctions, AIPAC said it would enhance Obama’s leverage in negotiations with Iran. Democratic and Republican Senate staffers both said this argument was a way to appeal to Democrats who did not want to be in open conflict with Obama. The president responded by saying he did not need such leverage and the sanctions bill would destroy the delicate negotiations with Iran.

Corker was one of three members of his party who did not sign Kirk’s letter. In an interview Monday, he said AIPAC members did not call him. He was not critical of other Republicans, but he said the letter would not get the Senate any closer to passing new sanctions on Iran that may preserve the economic pressure on the country that he assessed was dissipating during the negotiations.

Corker said AIPAC now “finds itself twisted in a knot.”

“Obviously they are trying to navigate keeping access to the administration and candidly their support of Israel and their support of the Democratic Party. They find themselves in a very tough spot,” he said.

But Republicans weren’t the only ones upset with AIPAC. In the instance of Debbie Wasserman-Schultz, the chairwoman of the Democratic National Committee, AIPAC sent a letter to supporters asking her to support the sanctions she was telling her constituents in Florida that she supported. The letter, however, included a link to a highly critical article about her from the Washington Free Beacon. A member of AIPAC’s national board and a donor to Wasserman-Schultz, Bruce Levy then criticized the letter in an interview with Foreign Policy magazine.

This incident came despite AIPAC’s concerted effort to woo Democrats for more than a decade. In 2003, the group authorized a study (known inside the organization as an internal strategic planning exercise) about how to reach out to core Democratic constituencies, according to former lobbyists for the organization. “AIPAC had been vexed for some years by allegations that it was tilted to the Republicans and had moved away from Democrats,” said Steve Rosen, the group’s former director of foreign policy who was fired by AIPAC in 2005 after the Justice Department alleged that he solicited classified information from a Pentagon analyst. In Obama’s first year in office the Justice Department dropped its prosecution.

Rosen said AIPAC at the time thought the charge that it was tilting right was “a false allegation,” he said, “it was repeated so often that something had to be done about it. This was an effort to build stronger links to many of the core constituencies of the Democratic Party.”

As a result of the study, AIPAC hired specialized staff to make the case for the Jewish state to Hispanics, blacks, Reform Jewish rabbis, and eventually even labor unions. (The exercise also resulted in a renewed effort to reach out to evangelical Christians, a core Republican constituency.)

But the price of bipartisanship in the Obama era at least has been an unwillingness until recently to openly oppose the president. For example, despite the opposition of many Republicans and other pro-Israel groups such as Christians United for Israel, AIPAC chose last January not to weigh in on the nomination fight of Chuck Hagel, the current defense secretary. In September, after President Obama said he would be seeking a war authorization from Congress to strike Syria, AIPAC lobbied Congress for the resolution at the request of the White House. At the time, even the Israeli government was reticent about AIPAC’s push for the resolution, according to one former senior Israeli official.

When AIPAC supported the Kirk-Menendez sanctions bill over the objections of the White House, it marked a new phase for the lobby. “There are a lot of Democratic senators who are up for election this year,” one Republican Senate staff member said. “I bet they would vote against the White House if AIPAC pushed for a vote.”

That vote may eventually come. On Friday, AIPAC President Michael Kassen issued a statement he said he had hoped would clarify what he said was a mischaracterization that AIPAC no longer supported the Kirk-Menendez legislation. “We still have much work to do over the coming months,” he said. “It will be a long struggle, but one that we are committed to fighting.”

Republicans appear keen on fighting that struggle as well. But it’s not clear whether they will be taking direction from the lobby anymore.