Peter Beinart writes: In Chicago, Barack Obama lived across the street from a very unusual synagogue, KAM Isaiah Israel, and its very unusual rabbi, Arnold Jacob Wolf. Wolf had been the founding chairman of Breira, the first American Jewish group to advocate a Palestinian state, and throughout his career, he passionately challenged Israeli settlement policies and the American Jewish organizations that justified them. In 1970, in words that could have been written this morning, Wolf denounced American Jewish leaders who, on the issue of Israel, “do not demand support, but rather submission…Any congregation whose allegiance is the least bit critical, any rabbi who holds independent views of the Middle Eastern situation, is eyed with suspicion, if not with downright hatred.”

Wolf liked Obama, but considered him timid. One month before Obama’s election, and three months before Wolf’s death, the octogenarian rabbi predicted that although Obama “knows more than most people do about the [Middle East] situation…he’s going to go very cautiously and not do anything that shakes up the Jewish community. I’m not sure I agree with that, but that’s what’s going to happen.”

Wolf was right. Obama has been cautious. He’s put far less pressure on Benjamin Netanyahu to stop settlement growth than George H.W. Bush put on Yitzhak Shamir. He’s been far more indulgent of Netanyahu’s war in Gaza than Ronald Reagan was of Shamir and Menachem Begin’s war in Lebanon.

But although Obama has not changed the American debate over Israel, the Obama coalition has. Look at the polls taken during this war. A majority of Americans defend Israel’s actions and blame Hamas for the violence. But among the demographic groups that backed Obama most strongly, it’s the reverse. First, young people. According to Gallup, while Americans over the age of 65 support Israel’s actions by a margin of 24 points, Americans under 30 oppose them by a margin of 26 points. Second, racial and ethnic minorities. White Americans back the war by 16 points. Non-whites oppose it by 24 points. Third, liberals. According to the Pew Research Center, conservatives are 54 points more likely to blame Hamas for the fighting than Israel. Among liberals, it’s tied.

What do young people, minorities and liberals have in common? They’re the constituencies whose overwhelming support made Barack Obama president.

In Washington, Democratic politicians from Obama on down still overwhelmingly support Israeli actions. Earlier this month, the entire United States Senate — including socialists like Bernie Sanders and progressive firebrands like Elizabeth Warren — supported a resolution on Gaza so one-sided that it didn’t even acknowledge any Palestinians had died.

But if Sanders and Warren haven’t changed, the people who vote for them have. One can still find older commentators like Alan Dershowitz and Abe Foxman who defend Israel’s actions in Gaza while championing a liberal agenda inside the United States. Among younger pundits, by contrast, that combination has virtually disappeared. One of the last holdouts was New York Magazine’s Jonathan Chait, a highly regarded critic of Republican domestic policy who over the years has generally blamed Palestinians more than Israel for the ongoing conflict. Yet earlier this week, in a widely discussed column, Chait wrote that “it has dawned on me that I am one of the liberal Jews who…has grown less pro-Israel over the last decade.” Among younger Americans, including younger American Jews, “liberal except on Israel”—once a common political identity — barely exists.

The result is that in the media, if not in Congress, the debate over Israel’s behavior is mostly playing out along partisan and ideological lines. The strongest defenders of Israeli actions are generally conservative Republicans who oppose a Palestinian state. On social media, defenses of Israeli behavior are frequently laced with hostility toward President Obama and toward Muslims, which is not surprising given that, according to one recent poll, 63 percent of Republicans believe Islam is incompatible with American values. But in America’s hyper-polarized political environment, the more conservatives defend Israeli policy in terms Obama voters find alienating, the more alienated Obama voters grow from Israeli policy. The more enthusiastic Sean Hannity and John Hagee become about this war, the more Obama voters decide it must be wrong.

And it is Obama voters — not Hannity and Hagee supporters — who are growing as a share of America’s population. In the United States, Israel has the same demographic problem as the GOP. Every year, older whites decline as a share of America’s adult population. Every year, Millennials and minorities — the two groups most skeptical of Israeli behavior — grow.

The America that exists in Netanyahu’s head — an America populated by conservative, fervently nationalistic, white Christians who believe the civilized West must wage a global war against barbaric Islam — is slowly dying. On questions of culture, war and peace, younger Americans often think more like their European counterparts than their own parents and grandparents. In 2013, for instance, Pew found that Americans under 30 were 24 points more likely to approve of the United Nations than were Americans over 50, the largest age gap in any of the seventeen countries Pew surveyed. A 2012 Pew poll found young Americans 30 points more likely than their elders to say the United States should “avoid military confrontation” with Iran rather than “take a stand.” And according to a 2011 Pew poll, while Americans over 50 were far more likely than Western Europeans to say “our culture is superior to others,” Americans under thirty were actually less likely to say so than young people in Britain, Germany and Spain. Not coincidentally, young Americans are far less religious than their elders too.

As America grows less nationalistic, less hawkish, less religious and less inclined to consider its own culture superior, it will grow less sympathetic to an Israeli government defined by exactly those characteristics. When will that change American policy? I don’t know. As the gun control debate shows, well-organized, passionate constituencies can wield tremendous influence in Washington even as public opinion shifts against them. When it comes to Israel, older, more religious American Jews and older, more religious white Christians are such a constituency. And they will keep punching above their weight for many years to come.

But every time a conflict like this breaks out—especially if Israel continues to elect governments hostile to a viable Palestinian state—the American mood will incrementally shift. Already, Israel has lost Jon Stewart, the most influential spokesperson for America’s liberal young. By the next Gaza War, if God forbid it comes, Israel will have lost MSNBC too. And eventually, the political fears that have restrained Obama will not restrain his ideological successors.

I fervently hope that when that shift comes, it will bring a shift in American policy towards the occupation and not a weakening of America’s commitment to Israeli security, as expressed in systems like Iron Dome. And I fervently hope that when it comes, there will still be a two state solution to pursue. Somewhere, I suspect, Rabbi Arnold Jacob Wolf, of blessed memory, is hoping that too.