The rest of his answer, about a planned post-Christmas trip to Israel, was interrupted by scattered jeering. Trump turned to a heckler near the front of the Ronald Reagan Building's ballroom whom he could hear clearly.
"Who's the wise guy?" asked Trump. "Just relax. You'll like me very much, believe me."
The subject of Jerusalem was raised in a question, inspired by a fresh interview with the Associated Press in which Trump refused to commit to any preconditions in negotiations between Israel and the Palestinians.
Trump's speech to the RJC followed in that theme. Trump drew loud applause when criticizing Secretary of State John Kerry ("the worst negotiator") or the Obama administration in general ("the worst thing that's happened to Israel"). But even a specific follow-up question about what Israel might need to give up at the negotiating table was met with a cannonade of non-answers.
"It’s perhaps the hardest deal in history to put together," said Trump, asked specifically whether Israel should return to pre-1967 borders. "I don’t know that Israel has the commitment to make it. I don’t know that the other side has the commitment to make it. With that being said, I have a good chance."
The meandering answer seemed to loosen Trump's grip on the room, and it contrasted with his patter about the weak negotiating skills of the Obama administration. After spending several minutes saying Americans should have demanded the release of prisoners before even sitting down with Iran, Trump was chastising anyone who thought Israel and Palestine could negotiate with terms like the state of Jerusalem already decided.
"You can't go in with that attitude," he said. "If you're going to make a deal — and you can make a great deal — you can't go in with the attitude that you're going to shut it down. You've got to go in and do it nicely so everyone's happy."
The Republican front-runner went on to praise the negotiating acumen of Jewish businessman — a constant refrain in his extemporaneous remarks.
Later, after suggesting that the shootings in San Bernardino, Calif., might have been carried out by "radical Islamic" terrorists, Trump bemoaned that "we have a president that refuses to use the term" and thus keep the country safe.
"He refuses to say it," said Trump. "There's something going on with him that we don't know about."
That line got a round of applause; a question to Trump's campaign, about what he was referring to, was not immediately answered. Trump did clean up some of the Israel chatter by saying the world was not aware of what the country had been forced to trade away.
"The public relations for Israel hasn’t been so great," he said. "Israel’s given a lot, but hasn’t been given credit. Some things have been given that have been unthinkable."
After the speech, conservative activist Gary Bauer said that Trump had lost momentum by refusing to give a clear answer on Jerusalem.
"When it started, they were skeptical, and you could feel the room warming to him," Bauer said. "I think he turned a lot of people. And then he lost them, because he couldn't just say, 'Of course, Jerusalem is the capital, we won't negotiate on that.' "