“Jeb said: ‘We were safe with my brother. We were safe,’” Mr. Trump said on the program. “Well, the World Trade Center just fell down! Now, am I trying to blame him? I’m not blaming anybody. But the World Trade Center came down. So when he said, ‘We were safe,’ that’s not safe. We lost 3,000 people, it was one of the greatest — probably the greatest — catastrophe ever in this country, if you think about it, right?”

While speaking ill of the second President Bush might pay off in a general election, New York Times/CBS News polls suggest that it might not be wise in the campaign for the Republican nomination. Support for the former president remains high among loyal G.O.P. voters. When George W. Bush left office in January 2009, 72 percent of Republicans (but only 26 percent of Americans) viewed him favorably, and in April, that number was unchanged among Republicans (and had risen a bit, to 30 percent, among all Americans).