“There comes a time when if we pursue justice and peace, we are going to have to say that Netanyahu is not right all of the time,” Mr. Sanders said, referring to the Israeli prime minister, amid cheers from the crowd at Thursday’s Democratic debate in Brooklyn. He added: “All that I am saying is we cannot continue to be one-sided. There are two sides to the issue.”

Jewish Democrats, like the rest of the party, have been struggling for years over the appropriate level of criticism when it comes to Israel’s policies in the occupied West Bank and Gaza. But that debate burst onto a big national stage this week thanks to Mr. Sanders, the most successful Jewish presidential candidate in history.

Mr. Sanders’s comments, in the de facto capital of Jewish American politics, buoyed the liberal and increasingly vocal Democrats who believe that a frank discussion within the party has been muzzled by an older, more conservative Jewish leadership that is suspicious of criticism of Israel.