In 1962, U.S. President John F. Kennedy told Israeli Foreign Minister Golda Meir that the United States and Israel had a “special relationship.” A hallmark of that relationship has been its bipartisan nature, which has been reinforced by powerful lobbies working in unison on both sides of the political aisle. Such support made it possible for the United States to send Israel $121 billion in foreign aid between 1948 and the end of 2014—more than to any other country. The United States also backed Israel in its regional conflicts and vetoed or opposed United Nations resolutions critical of Israel’s occupation of the West Bank.

But there are growing signs of discord within that community that could, in turn, threaten the special relationship. The most recent is the rift created by House Speaker John Boehner’s decision to invite Prime Minister Benjamin Netanyahu, the head of the Likud Party, to speak before Congress on March 3 without consulting beforehand the White House or congressional Democrats.

The division between Republicans and Democrats over Israel did not, however, emerge overnight with Boehner’s invitation to Netanyahu. Indeed, the story begins before the founding of Israel. During U.S. President Franklin Roosevelt’s administration, most American Jews and American Zionists became Democrats, and Zionist organizations relied on the connections that the prominent Democrats—notably, Supreme Court Justice Louis Brandeis and Rabbi Stephen Wise—had with Roosevelt. But in 1944, Cleveland Rabbi Abba Hillel Silver took command of the American Zionist Emergency Council, which was formed in 1939 as a coalition of various Zionist organizations. He established a policy of seeking bipartisan endorsements for a Jewish state, using the threat of endorsing Republicans who favored a Jewish state to pressure the Truman administration into supporting its cause.

The Israel lobby in Washington evolved out of Silver’s strategy. After Israel’s founding in 1948, the coalition spun off into the American Zionist Council, a collection of 21 different Zionist groups, to lobby Washington; and in 1963, the council, which was under investigation for acting as a covert foreign agent, reincorporated as the American Israel Public Affairs Committee (AIPAC). It initially worked in tandem with the Conference of the Presidents of Major American Jewish Organizations, which had been founded in 1954: AIPAC lobbied Congress, and the Presidents’ Conference lobbied the White House. But by the 1980s, AIPAC was increasingly encroaching on the conference’s turf.

During most of the half century after Israel’s founding, both parties in Congress backed aid to Israel and supported its government. There were conflicts over specific issues. For instance, in 1981, 36 of 46 Senate Democrats opposed and 42 of 54 Senate Republicans supported the sale of Airborne Warning and Control System (AWACS) aircraft to Saudi Arabia, which AIPAC and Israel opposed. But that remained an isolated issue and did not lead to partisan animosity over Israel.

The main change that occurred from the early 1980s to the early 2000s was the balance of power between Republicans and Democrats in the lobbying community and in congressional support for Israel’s government.

From 1948 until the early 1980s, liberal Democrats led the main lobbying organizations, and Democrats were the main champions of aid to Israel in Congress. When there was a difference over aid to Israel, as in the case of AWACS or the foreign aid cuts also in 1981, Democrats took the lead in pressing for Israel’s interests. But two developments tilted things toward the Republicans. The first occurred in Israeli politics. The Labor Party, which was ideologically closer to the Democrats, controlled Israel’s politics from 1949 to 1977. From 1977 onward, it was the conservative Likud Party (in fact, Likud has been in power for 27 of the past 38 years, Labor for only eight, and a centrist party for three). Likud was closer to the Republicans in its domestic policy and in its foreign policy, which stressed a less compromising stand toward the Palestinians and Israel’s neighbors.

The second development was in American politics. In 1980, Republicans won the White House and Senate, and in 1994, Republicans finally won the House and Senate. Republicans have controlled the House, which initiates appropriations for foreign aid, for all but four of the last 21 years. Since AIPAC’s strategy was always based on maintaining support for Israel’s government in Congress, initially, that meant working primarily with Democrats. But after 1980, that started to change. After 1994, AIPAC was dealing with a whole new world. To reach the new leadership in Congress and the White House, AIPAC and the Presidents’ Conference began elevating leaders who were closer to the Republicans and to the Likud Party in Israel. That began in 1982, when AIPAC chose a Republican as its president. In 1993, AIPAC fired its executive director, Thomas Dine, a former aide to Senator Edward Kennedy, and replaced him in 1995 with a Republican candidate, Howard Kohr, who remains at the helm.

The first signs of partisan division over Israel began to appear in the 1990s. Although U.S. President Bill Clinton welcomed Israeli Prime Minister Yitzhak Rabin and Palestine Liberation Organization Chairman Yasir Arafat to the White House to sign the Oslo Accords, conservative Republicans sympathized with the Likud opposition to the treaty, as did some AIPAC leaders. In 1995, Congress Republicans passed the Jerusalem Embassy Act, which, by declaring Jerusalem an undivided city, threatened to undercut negotiations between the Israelis and Palestinians over East Jerusalem.

After Rabin’s assassination in November 1995, Republicans backed Netanyahu, who hired Republican campaign consultant Arthur Finkelstein to help him run his campaign in Israel’s 1996 election. Clinton sided with Labor candidate Shimon Peres. One month before the election, Clinton invited Peres to the White House to sign a defense pact. Once again in 1999, the two parties chose sides in the election. Clinton’s 1992 campaign manager James Carville and pollster Stanley Greenberg traveled to Israel to help Labor candidate Ehud Barak defeat Netanyahu, with whom Clinton had frequently clashed.

During this period, however, there was a discrepancy between the growing Republican tilt in Washington and public opinion. The most determined support for Israel still came from Jewish Democrats. But that began to change, too, after the September 11, 2001, terrorist attack. Some Republican evangelicals, citing biblical texts, had always been supportive of Israel, but after September 11, Christian support for Israel fused with opposition to radical Islam. In 2006, evangelical minister John Hagee founded Christians United for Israel, which now claims to have two million members. These Republicans sympathized with the Likud Party and the religious parties further right that opposed a Palestinian state. The growing Republican lean is reflected, too, in public opinion polls. In a Pew poll released last year, 54 percent of Republicans, compared with 15 percent of Democrats, said that the United States was “not supportive enough” of Israel.

The Republican Jewish Coalition, which was founded in the 1980s but was mainly active in trying to win wealthy Jews over to the party, became active in promoting Israel’s conservative government. Funded by casino mogul Sheldon Adelson, a big supporter of Netanyahu, it became a major player in the Republican Party. A generation of conservative Republican House members and senators also embraced the new evangelical outlook on Israel. They have introduced resolutions to allow Israel to annex the West Bank, to cut off all American assistance to the Palestinian Authority because it joined the International Criminal Court, and to pressure the State Department to move the U.S. embassy to an undivided Jerusalem.

In Israel, Netanyahu embraced the Republican lean in U.S.-Israeli relations. In 2008, he made Ron Dermer—a former Republican political consultant who had helped draft the Republican “Contract with America” in 1994 (a set of proposals that the party would enact if it took power)—his chief adviser and then, in 2013, his ambassador to the United States. Dermer helped arrange a visit by Republican presidential candidate Mitt Romney to Israel in the summer of 2012, and this January, he initiated the plan for Boehner to invite Netanyahu to address Congress on the eve of the Israeli election. In its ads, Netanyahu’s party flaunted its defiance of the Obama administration. Meanwhile, Republicans in Washington promised to “stand with Israel,” and one prominent Republican analyst and commentator, William Kristol, called on attendees at the AIPAC conference to boycott speeches by Obama administration officials.

The Democrats, for their part, no longer unequivocally support the Israeli government. Jeremy Ben-Ami, a former Clinton aide, founded J Street in 2008 as a counterweight to AIPAC in Washington. It advertises itself as the “home for pro-Israel pro-peace Americans.” As the Obama administration moved into outright opposition of the Netanyahu government, J Street moved with it. After the breakdown of the peace talks last spring, the organization called for Netanyahu’s removal and for Netanyahu to cancel his visit to the United States. In the past, AIPAC was able to vanquish similar rivals such as Breira and New Jewish Agenda, but J Street has lasted and grown. It now has a following among Capitol Hill Democrats.

AIPAC’s budget dwarfs that of J Street, but the new organization has growing support among Democrats and Jewish Democrats. In a Gallup poll, 83 percent of Republicans compared with only 48 percent of Democrats said they sympathized more with the Israelis than the Palestinians. A Pew poll in 2013 of American Jews found that 44 and 17 percent, respectively, believed that continued building of settlements “hurts” rather than “helps” Israel’s security.

In Congress, there is still bipartisan support for foreign aid to Israel. Last summer, the House passed by 395 to eight a bill that gave Israel $225 million in military aid to repair its Iron Dome missile system after the brutal war in Gaza. The bill passed the Senate by unanimous consent. But the bipartisan consensus has been shattered over the negotiations that the United States, along with Great Britain, France, Germany, China, and Russia, is conducting with Iran. In November 2013, the countries reached an interim agreement that set terms for a final agreement. If a final agreement is reached, it will not be subject to Senate ratification. And although Obama believes he can suspend Iran sanctions without congressional approval, he can’t permanently end them without congressional support.

The Netanyahu government opposed the interim deal that the powers struck with Iran because it didn’t offer a complete dismantling of Iran’s nuclear facilities, including its ability to produce civilian energy. In the fall of 2013, AIPAC lobbied for a bill that would have required Iran to meet Israel’s stringent terms and would have required the United States to “stand with Israel” if Israel decided to attack Iran. The bill, sponsored by Republican Mark Kirk and Democrat Robert Menendez, won the support of 43 of 45 Republicans, but only 16 of 55 members of the Democratic caucus. J Street also opposed the bill. And when Obama threatened to veto the bill, should it cross his desk, in his State of the Union address, several more Democrats, including Menendez, backed off. Senate Majority Leader Harry Reid said he wouldn’t bring the bill to a vote.

This January, with negotiations nearing a final March 24 deadline, the same drama played out again. Kirk and Menendez introduced a bill threatening new sanctions if the negotiations didn’t bear fruit by the deadline. But then Menendez and nine other prominent Democrats sent a letter opposing a vote on the bill, at least until late March. Though if an agreement with Iran is reached, Republicans have prepared to do battle. Senator Bob Corker, the new Republican chairman of the Senate Foreign Relations Committee, has introduced a bill that would require Obama to present the agreement for Senate approval and to withhold any suspension of sanctions for 60 days. Obama has threatened to veto this measure as well.

Some of the Democratic support in Congress for the Iran negotiations is probably out of loyalty to the president. Menendez’s decision to postpone a vote was certainly out of deference to Obama. But allegiance can’t explain the refusal of 70 percent of Democratic senators to back a sanctions bill in January 2014 that AIPAC lobbied strenuously for and that reflected a position the Israeli government had loudly and consistently advocated. There is no comparison between Israel’s opposition to the AWACS sale, which was short-lived, and its strident and long-standing opposition to a nuclear agreement with Iran.

In her speech to the AIPAC conference, UN Ambassador Samantha Power said, “We believe firmly that . . . the U.S.-Israel partnership transcends politics and it always will.” But with the fracas over Netanyahu’s visit, and the continuing battle over the Iran negotiations, the era of automatic bipartisan support for Israel’s government is drawing to a close, and with it, perhaps, the special relationship between the United States and Israel. Bipartisan support is also ending on an odd note since Democrats, who were once the staunchest supporters of Israel’s government, have become its critics, while the Republicans, buoyed by evangelical fervor, have become its most enthusiastic backers.