Last week, the House of Representatives adopted H.R. 246, a nonbinding measure condemning the boycott, divestment and sanctions (BDS) movement against the Israel, by a vote of 398 to 17. The vote shows how strong support for Israel remains in Congress — while also revealing how concerned Israel’s advocates are about the potential for quickening criticism of the country and its policies.

Old-school pro-Israel activists are sounding the alarm that the party of Reps. Ilhan Omar (D-Minn.) and Rashida Tlaib (D-Mich.) is becoming “Corbyn-ized” -- a reference to British Labour Party leader Jeremy Corbyn. They fear the emergence of a party that is pro-Palestine and no longer pro-Israel, and not without cause. Sen. Bernie Sanders (I-Vt.) makes campaign stops to pose for smiling pictures with “Jews Against the Occupation” and calls the government of Israeli Prime Minister Benjamin Netanyahu “racist.”

Such behavior from a major presidential contender was unthinkable a short time ago, and indicates how some American Jews, and many younger Democrats, are ready for new directions on Israel–Palestine.

Young liberals, some with socialist leanings and many with more sympathy for Palestinians than for Israel, are repopulating the Democratic Party. Increasingly, they view the half-century-long Israeli occupation of lands conquered in 1967 as irreversible.

Meanwhile, liberal Jewish groups such as IfNotNow and the new Progressive Israel Network hope to seize this moment to press Democratic presidential aspirants on their plans for putting muscle into the U.S. government’s longstanding support for Israeli withdrawals from the occupied territories.

But some liberals and progressives may be unaware of how deep the Democrats’ institutional commitment to Israel runs, and how difficult it will be to change.

For almost 40 years after the State of Israel was founded in 1948, Israel was a liberal cause in American politics. Democrats supported Israel far more than did Republicans. And liberal Democrats such as Eleanor Roosevelt and Hubert Humphrey were the staunchest of all of Israel’s American allies. Labor leaders made pilgrimages to Israel to celebrate this Middle Eastern social democracy, ruled by a dominant Labor Party until 1977.

For liberals who had come of age in the 1940s, the issue of anti-Semitism had a generational significance akin to that which racism and civil rights would occupy among later cohorts of liberals. For the World War II generation, to be pro-Jewish, especially in the shadow of the Holocaust, meant believing in Israel — not just in the rightness of its existence, but in its status as a beacon of progress and moral heroism in the Middle East.

During the 1950s and 1960s, Israel fit neatly into the ideological battles in American politics as these liberals championed Israel, and many Republicans, as well as conservative Democrats, thought U.S. interests lay more with Arab states. This alignment meant that, during this period, Israelis feared that Republican governments, especially the Eisenhower administration, were pro-Arab. But Richard Nixon and then, even more, Ronald Reagan pushed the GOP to a more pro-Israel position in the 1970s and 1980s. They began to see Israel as a valuable ally in worldwide battles against communism and terrorism.

While President George H.W. Bush had a sometimes difficult relationship with Israel, during the presidency of his son, George W. Bush, the era of GOP love for Israel blossomed fully. End-time prophecy belief among conservative evangelicals, increasingly powerful in Republican politics, as well as an aggressive counterterrorist attitude that saw in Israel a model for America, helped to move the GOP in a stronger pro-Israel direction. Bush sometimes bristled at aggressive Israeli actions, but by the early 2000s, his own party’s members of Congress were more likely to side with Israel than him in a conflict. When America invaded Iraq in 2003 and deposed Israel’s longtime foe Saddam Hussein, Bush secured his stature as a pro-Israel leader for the ages.

But flowering conservative support for the Jewish state did not destroy Democratic affinities for Israel — certainly not at the leadership level.

And so, by the turn of the 21st century, pro-Israel politics had become bipartisan. Today, controversy over Israel and Palestine is shaped less by partisanship than by differences in age, race and ideology. Younger liberals, perhaps especially young people of color, are the engines of rising discontent with reflexively pro-Israel policy. They often struggle to understand, much less to embrace, the way that older liberals see Israel.

Since these groups reside almost entirely in the Democratic Party, they have become a problem for that party’s leaders to manage. But their views do not yet threaten Israel’s unique position in bipartisan policymaking. Today’s top Democrats, who inherited their fealty to Israel from the titans of Cold War liberalism, have their own history of taking staunch pro-Israel positions that many forget or do not know.

Consider the signature issue of Trump’s pro-Israel policy, his relocation of the U.S. Embassy in Israel from Tel Aviv to Jerusalem. This outraged diplomats and scandalized many young liberals.

Yet the Democratic Party first supported moving the embassy to Jerusalem in its 1976 convention platform — a full 20 years before the GOP followed suit. Trump’s position started as a Democratic position, and it became a bipartisan position when Congress, with strong votes from Republicans and Democrats, in 1995 foisted the Jerusalem Embassy Act on a nervous Bill Clinton.

Or take Rep. Eliot Engel (D-N.Y.), who denounced Omar after she mocked fellow members of Congress for supposedly being susceptible to the power of pro-Israel money. A 30-year incumbent, Engel chairs the House Foreign Affairs Committee. His views on the Middle East are today more like those of the GOP than of the Democrats — while 76 percent of Republicans sympathize more with Israelis than Palestinians, only 43 percent of Democrats do. Engel approved the embassy move, voted against President Barack Obama’s Iran nuclear deal and supported the Iraq invasion (which he later regretted) and opposes anything more than superficial criticism of Israel.

A product of public housing and public schools who became a public-school teacher, Engel also champions Great Society programs down the line and supports single-payer health care and the Green New Deal. This, combined with his Trump-like views on Israel and Palestine, may make him seem contradictory to young liberals.

Yet during most of the post-1948 period, Engel’s package of views would have been no contradiction at all. Engel represents what Democratic Party liberalism used to be, including a fierce partisanship for Israel. The reigning elites of his party’s gerontocracy remain rooted in that earlier formation.

Today’s trends may spell the eventual demise of Democratic support for Israel. But eventual does not mean imminent. In the past five presidential elections, American Jews have given the Democrat, on average, 74 percent of their votes. In light of this strong Jewish support, the Democrats are not likely to get tough on Israel anytime soon, and the party’s leaders probably calculate that Jewish liberals, who may be relatively alienated from Israel, can be taken for granted in 2020.

Right now, Israel sits in the sweet spot of enjoying full-bore Republican support plus elite Democratic backing in Washington. That alignment has prevailed for about 25 years. While several Democrats running for president have tried to keep their distance from the most ardent pro-Israel groups for now, only Sanders seriously promises to take U.S. policy in a new direction. Israel’s advocates, sensitive to the realities of American politics, may move now to extract the maximum benefits for Israel before the window of bipartisan support narrows further.