The comment, delivered at a forum of Republican Jewish fundraisers and activists in Washington, was made in response to the rampage in San Bernardino. It was one of several remarks and themes in Trump's improvised speech on Thursday that showed his ability to make provocative statements that would likely land other presidential candidates in trouble, but seem routine in the context of Trump's campaign.
The speech by Trump, the real estate magnate, was also notable for touching on Jewish stereotypes – with references to money and negotiating skills -- that drew rebukes from some Jewish conservatives on Twitter but were received with some laughter from the audience.
Trump spoke at a forum of the Republican Jewish Coalition, a group of powerful
Wednesday's massacre in San Bernardino put an added focus on the issue of domestic terrorism. While authorities have not determined whether it was inspired by or connected to jihadist terrorism, many candidates spoke about that threat while discussing the attack.
Trump said Wednesday's attack "probably was related" to Islamic terrorism, while leaving some room for doubt.
"It always happens," was how he characterized his first reaction to the attacks, suggesting he viewed the massacre as a random act of violence and not a planned terrorist attack.
"When I heard about it, I figured probably not," he said. "But it turns out, probably related."
"Radical Islamic terrorism," he added. "We have a president who refuses to use the term. Refuses to say it. There is something going on with him that we don't know about."
The White House avoids using the phrase to keep from alienating the world's billion or so Muslims, including Americans, as well as the leaders of crucial allies in the Middle East.
Trump's remarks were light on policy, with several comments that appeared to be efforts to connect with the audience, some of which caused raised eyebrows.
Trump noted that one of his daughters, Ivanka, is Jewish. She converted to the faith when she married. Other comments of his touched on long-standing Jewish stereotypes.
"I'm a negotiator, like you folks," he said at one point.
"You're not going to support me because I don't want your money," he said at another.
Trump drew mostly laughs. But several people raised questions on social media. "What the hell does that mean?" tweeted Ari Fleischer, the former spokesman for George W. Bush.
There were boos when Trump declined to commit to recognizing Jerusalem as Israel's capital. Successive administrations of both parties have stopped short of that step, fearing it would be provocative in the Arab world. But many Jewish conservatives, who were heavily represented in the audience, see it as a priority.
Trump was also vague when asked which Arab leaders he could work with, mentioning the king of Jordan without using his name and then veering into other topics including his relationships with Democrats and others he has met during his career in real estate.
His biggest policy message was a critique of Obama – "the worst thing that's ever happened to Israel" – and the deal his administration and leaders of five other countries struck with Iran designed to limit its nuclear capabilities. Israeli Prime Minister Benjamin Netanyahu has said the pact is an existential threat to Israel.
Several activists who headed for lunch after Trump's talk said they did not think much of his speech but were not offended, with one man noting that Trump was introduced as mishpucha, the Yiddish word for family.
"It was in jest," said Andrew Friedman, a Los Angeles attorney who is president of his synagogue. "He shoots from the hip."
"Irreverence is good," said Eric Levine, a New York attorney who is raising money for Florida Sen. Marco Rubio's campaign. "What offends me is his complete lack of knowledge."
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