WHETHER IT was a major diplomatic slight or a minor one overblown by media coverage, what happened to Representative William Delahunt in a congressional trip to Israel last month was telling.

Because the trip was sponsored by J Street, a “pro-Israel, pro-peace’’ organization that has criticized the Israeli government, Israel’s minister of foreign affairs, Avigdor Lieberman, and his deputy, Danny Ayalon, refused to meet with the five congressmen as long as J Street and another pro-peace sponsor was present. The message was clear: Your traveling companions have criticized us, so we won’t sit with you unless you keep them away from the table.

Israel’s government certainly has the right to choose who it talks to. But its actions show it to be a step behind the changing composition and attitudes of American Jewry. At a time when many American Jews are feeling fewer compunctions about criticizing Israel, and are often less concerned with external threats posed by Iran and Israel’s other enemies than the demographic time bomb it faces as its Palestinian population expands, what it means to be “pro-Israel’’ is changing, particularly among younger Jews.

There are still plenty of young American Jews who take pride in wholeheartedly supporting the Israeli government. But this view isn’t nearly as dominant as it once was, and research by Steven M. Cohen of Hebrew Union College helps show why. Cohen found that younger Jewish professional and religious leaders tend to be less likely to see Israel as threatened by its neighbors, and therefore less worried about Israel’s security.

The idea that being an American Jew doesn’t necessitate lockstep support for Israel, and that Israel is strong enough to withstand criticism from the outside world, were on full display last week at Harvard’s Hillel House, which hosted a talk by J Street’s head, Jeremy Ben-Ami.

In an interview before the event, Ben-Ami talked about the changing experience of being an American Jew.

“If you’ve had personal experience - if not you [then] at least your parents - with the destruction of your people, you’re more likely to take it as a possibility that it could happen again,’’ he said. “If you have grown up here in complete comfort and safety and no one you know in an immediate sense has been through that, I do think [you’re] going to have a very fundamental[ly] different view, a different take, on how you view the Iran threat.’’

This different, less fearful view of things came through clearly in some of the young members of the audience.

For instance, when asked about the prospect of Iran destroying Israel,Harvard Divinity School student Kenan Jaffe, 26, said he thought it was “unlikely.’’

“I also don’t think it’s directly related to the Palestinian question,’’ he said, “and it is only to the extent that if Israel comes to a final status solution with the Palestinians, Iran will have nothing to say about Israel and no reason to make threats against it.’’

This is a far cry from the notion of a bloodthirsty, implacable Iran fueled only by hatred for Israel - a story we hear quite often from groups like the American Israel Public Affairs Committee. And while most members of the audience probably weren’t as sanguine about Iran as Jaffe, fear of Mahmoud Ahmadinejad wasn’t, for the most part, what had brought them to Cambridge on a rainy February evening.

Rather, they were worried about the grim prospects that face Israel if it can’t make peace with the Palestinians. Given the region’s demographic patterns, absent a two-state solution, Israel will soon have to choose between being a Jewish state and a democratic one.

While J Street does strongly oppose the possibility of Iran getting nuclear weapons, the demographic crisis, not an attack from Iran, is the greatest threat facing Israel, said Ben-Ami.

He’s not alone in thinking so, if the popularity and early clout of his organization, which is just two years old, is any indication. And regardless of one’s political affiliation, this shift is going to have huge ramifications for the future of US-Israeli relations. If Israel wants to continue turning its back on those who criticize it, it may soon find itself with little to say to an increasingly large, vocal segment of American Jews.

Jesse Singal, a frequent contributor to the Globe opinion pages, can be reached at jsingal@globe.com.

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