The threat to President Joe Biden’s reelection from progressive critics of his support of Israel’s war in Gaza replicates a familiar pattern that jeopardized the prospects of past Democratic candidates.

Party progressives critical of Biden showed significant support in several Democratic presidential primaries this spring. But recent polls indicate most Democrats strongly back the president’s reelection and, in fact, his support is solidifying.

In past elections, progressive resistance stemmed from differences over issues like U.S. support for military actions overseas — as is the case this year — or the extent of government support for health coverage at home. The former fueled liberal challenges to President Harry Truman and former Vice President Hubert Humphrey, the latter to President Jimmy Carter and Hillary Clinton.

In 1948, former Vice President Henry Wallace challenged Truman’s firm stance against the Soviet Union’s expansionist policies. But he failed to prevent Truman from narrowly winning in a four-way contest that included Republican Thomas Dewey and states’ rights independent Strom Thurmond.

In subsequent elections, however, liberal resistance was more successful, helping to cause the defeats of Humphrey in 1968, Carter in 1980, Al Gore in 2000 and Clinton in 2016. The U.S. role in Vietnam was the issue in 1968, health care in 1980 and 2016, and environmental policy in 2000.

Biden hopes that, by raising the specter of former President Donald Trump’s threat to women’s rights and American democracy, he can replicate Truman’s 1948 success in surmounting both Wallace’s challenge from the left and Thurmond’s from the right.

This year’s progressive challenge to Biden, like those to Truman and Humphrey, reflects opposition to his muscular foreign policy, primarily his support of Israel’s war in Gaza but also his efforts to help Ukraine resist the 2022 Russian invasion.

Though the issues and the geography are different, it resembles the left-wing opposition to the U.S. role in Vietnam. At that time, U.S. progressives championed the Communist government of North Vietnam over the repressive, U.S.-backed South Vietnamese regime.

Today’s leftist groups are both campaigning for Palestinian rights and condemning Israel’s policies in Gaza and Israel itself. While many back Israel’s right to defend itself after Hamas’ brutal October invasion, they accuse the Israelis of genocide for killing thousands of Palestinian civilians, destroying much of Gaza and blocking international relief efforts.

In a lengthy report on the left-wing resistance to Biden, The New York Times said last Saturday that support for the Palestinians has become “a defining issue of the Democratic left,” including among groups that previously concentrated on domestic issues like climate change, housing and immigration.

Rather than the individual opposition of isolated groups, it said, “the pro-Palestinian movement is now propelled both by longtime — and sometimes hard-line — activists and by mainstream pillars of the Democratic coalition.”

That was underscored last week when a dozen liberal organizations and labor unions urged Biden to end military aid to Israel until it lifts restrictions on humanitarian aid for Gaza.

The group included progressive groups like MoveOn and the Working Families Party and more mainstream Democratic organizations like the Center for American Progress and NextGen America, founded by billionaire environmentalist Tom Steyer. It also included two prominent pro-Democratic labor unions, the Service Employees International Union and the National Education Association, both of which have endorsed Biden’s reelection.

A new poll by The New York Times and Siena University showed a plurality of registered Democrats said they sympathize more with the Palestinians than the Israelis. That position is especially strong among voters 18-29, who back the Palestinians by a 3-to-1 margin. By contrast, Democrats over 65 favor Israel by a similar 3-to-1 margin.

As a result, the poll showed that voters under 29 are evenly split between Biden and Trump, even though the former president is at least as pro-Israel as is Biden and those voters consider themselves more Democratic than Republican and more liberal than conservative. But it also showed Biden offsetting his problem with younger voters by making gains among other significant segments of the Democratic base. In the past six weeks, the poll said, Biden’s support has gone up 7 points among women, 3 points among Blacks and 10 points among Hispanics. As a result, he narrowed Trump’s advantage among registered voters from 5 points to a statistically insignificant 1 point.

In recent weeks, while maintaining his support for Israel, Biden has reacted to his liberal critics by stepping up pressure on Israeli Prime Minister Benjamin Netanyahu to allow increased humanitarian aid to Gaza, abandon plans to attack the city of Rafah and show restraint after last weekend’s Iranian drone attack.

That won’t satisfy critics who want to stop U.S. military aid to Israel and hope to influence the party’s platform when the Democratic National Convention meets this August to renominate Biden and Vice President Kamala Harris. Significant anti-Biden demonstrations there seem almost inevitable.

Politically, a lot may depend on what the Israelis do in the ensuing months and the administration’s reaction. But Biden will certainly maintain his basic pro-Israel position, even at the cost of some support from younger Democratic voters.

At present, given his improved standing in the Times/Siena poll and other recent surveys, Biden’s strategists may well believe he can surmount that resistance. But regaining more of their support would certainly make his re-election easier and prevent him from suffering the fate that befell Humphrey, Carter, Gore and Hillary Clinton.

Carl P. Leubsdorf is a former Washington bureau chief of The Dallas Morning News.