This year’s wave of liberal activism has seen Democrats work to protect Lyndon B. Johnson’s core domestic policy achievements, such as Medicaid and the Voting Rights Act. At the same time, however, the party’s base has fled from one of the few elements of Johnson’s foreign policy agenda that remained Democratic orthodoxy for decades after he left office: sympathy toward Israel.

Before the early 2000s, Democrats supported Israel in almost equal numbers to their Republican counterparts. But a backlash against President George W. Bush’s adventurism in the Middle East, the fraught relationship between President Barack Obama and Benjamin Netanyahu, and ideological conflict among liberals shattered uniform Democratic support for Israel at precisely the moment when conservative support for Israel spiked thanks to changing attitudes among evangelical Christians.

Twenty-first century civil rights activists view Palestinians as a marginalized population deserving of the same level of support as marginalized groups in the United States, despite the reactionary social policies of Hamas and the Palestinian Authority. Older generations of liberals, by contrast, welcomed a Jewish state after the Holocaust and identified Israel as an embattled, left-of-center democracy surrounded by dictatorial foes.

Even as backing for Israel from rank-and-file Democrats faded, until recently nearly all elected Democrats remained steadfastly supportive. But the actions of Sens. Kirsten Gillibrand (D-N.Y.) and Cory Booker (D-N.J.) in recent weeks indicate that ambitious elected Democrats are now starting to fall in line and adopt a far less pro-Israel position.

The extent of this shift provides a contrast to the Johnson years, when U.S. support for Israel first reached modern levels. Johnson had close ties with prominent pro-Israel Democrats from his time as Senate majority leader. He also shared an idealistic view of Israel as a bastion of democracy in the Middle East. On Israeli issues, he downplayed the nuclear nonproliferation concerns that had created tensions between Israel and the Kennedy administration, and showed a surprising willingness to overrule his national security advisers.

In early 1965, for instance, Johnson broke a stalemate between the State Department and the Israeli government to ensure what was then the largest U.S. arms sale to Israel. He required that Israel drop opposition to a simultaneous arms sale to Jordan, and that members of the Israeli cabinet not exploit the sale for domestic political purposes, but he pushed the sale through.

During the Six-Day War, Johnson’s most important decision may have been something he didn’t do: He avoided making public recriminations after the inadvertent Israeli attack on the Liberty, which killed 34 U.S. crew members. After the war, Johnson consistently backed Israel at the United Nations, resisting Soviet efforts to substitute a U.N. demand for an immediate Israeli withdrawal from all occupied territories for a resolution pressing for a land-for-peace deal.

This support included abstaining from a 1967 General Assembly resolution condemning the Israelis for altering the status quo in East Jerusalem in the hopes of persuading other countries to follow course (only 17 countries did so). Quite unlike President Barack Obama’s 2016 decision to abstain from a Security Council resolution as a rebuke of Israel, Johnson abstained to protect Israel’s interests. He did so even knowing that this position would isolate the United States.

As president, Johnson both represented pro-Israel sentiments within the Democratic Party and contributed to Democrats’ increasingly positive view of Israel.

Between 1967 and 2002, Israel enjoyed consistent bipartisan support, subject to short-term fluctuations after crises, such as the 1982 intervention in Lebanon and the First Gulf War. Yet over the past fifteen years, the warm sentiments that Democrats felt for Israel during the Johnson years have faded.

The backlash against George W. Bush’s invasion of Iraq and the neoconservativism that propelled it shattered the bipartisan consensus on Israel. Nine points separated Republican and Democratic levels of sympathy for Israel in 2001; by Bush’s last year in office, the gap neared 30 points. Increased Republican support accounted for much of this gap, but Democratic sympathy for Israel also declined slightly.

A second, more significant downturn has occurred over the past decade. The tense Obama-Benjamin Netanyahu relationship, for which both sides (though particularly Netanyahu) deserved blame, clearly contributed to this shift. But demographics also play a powerful role. As the older, whiter Republican base remains committed to Israel, a younger and more diverse Democratic base concluded that support for Israel conflicts with its brand of identity politics. Pew polls from 2016 and 2017 showed that, for the first time, more liberal Democrats sympathized with the Palestinians than with Israel.

These changing conceptions of liberalism have had an effect. In the past, the blowback would have singed any Democratic politician who was openly anti-Israel. Today, however, Israel-bashing provides a political boost — as evidenced by Minnesota Rep. Keith Ellison.

In 2010, Ellison claimed that Israeli interests “governed” U.S. policy toward the Middle East; four years later, during the Gaza War, he was one of only eight House members who voted against emergency funding for the Israeli air-defense system. Even a decade ago, no one harboring such views would have had a prayer of being elected Democratic National Committee chairman. Yet this year, liberal activists coalesced behind Ellison, who narrowly lost the chairman’s election.

Last week, Ellison received strong applause from a crowd of liberal activists for declaring that “all of us in this room have got to defend intersectionality.” This once-obscure academic concept (Merriam-Webster added an entry for it only in April) contends that different forms of discrimination overlap, and must therefore be fought across the board. Increasingly, liberal activists have applied such an approach to the Israeli-Palestinian conflict.

Yet using this principle to rationalize support for the Palestinians can, as New York Times columnist Bari Weiss recently observed, justify some decidedly “illiberal” views. Women’s March co-organizer Linda Sarsour, for example, has maintained that Zionism and feminism are incompatible, even as she has praised Saudi Arabia’s treatment of women. And the anti-Zionist “pinkwashing” movement seeks to obscure the chasm between Israel’s generally strong record on LGBT issues and that of its Arab neighbors.

Even as the party’s base has grown estranged from Israel, most elected Democrats have remained steadfast in their support. Generational politics play some role, as the top three Democrats in both houses of Congress are products of a different political era, each arriving on Capitol Hill more than two decades ago. And the fact remains that Republicans, independents and conservative Democrats, a constituent base most legislators need, remain staunchly pro-Israel.

But the party’s activist base is having an impact. Two weeks ago, Gillibrand and Booker announced opposition to pro-Israel bills within a day of each other. Gillibrand withdrew her sponsorship of anti-BDS legislation after fielding hostile town-hall questions from activists organized by the far-left Jewish Voice for Peace. (The measure has troubled civil liberties advocates as well, but Gillibrand acted only after the town halls.) Booker, meanwhile, joined three other Democrats in voting against the Taylor Force Act, which seeks to address payments by the Palestinian government to imprisoned killers of U.S. and Israeli citizens, in the Foreign Relations Committee.

Both senators have presidential aspirations and understand that being staunchly pro-Israel is a liability with the Democratic base. In a party oriented around resistance to Trump, it seems unlikely that the situation will change anytime soon, given that Israel is one of the few countries worldwide that remains (somewhat) supportive of him. In a summer featuring a revival of Johnson’s vision in domestic affairs, his assumption of a clear connection between liberal principles and support for Israel seems like a product of a bygone era.