Trump regularly speaks with reporters at campaign events and often takes multiple questions in an impromptu manner, making his silence Friday all the more noticeable.
When asked by CNN after a rally at a local high school here if he thought the attacks were George W. Bush's fault, Trump, after pausing to listen to the question, walked away.
Minutes later, he again declined to say anything when asked to react to Bush's response on Twitter, ignoring at least half a dozen questions on the matter before driving away in his motorcade. He did respond to questions about the crowd size at his campaign event Friday and why he was campaigning in Massachusetts.
The controversy began Friday morning when Trump implied that the former presidentcould share some blame for the attacks that killed nearly 3,000 Americans, as he was in office at the time.
"When you talk about George Bush, I mean, say what you want, the World Trade Center came down during his time," Trump said on Bloomberg TV.
Bloomberg anchor Stephanie Ruhle interjected, "Hold on, you can't blame George Bush for that," before Trump stood by his comments.
"He was president, OK? ... Blame him, or don't blame him, but he was president. The World Trade Center came down during his reign," Trump said.
Jeb Bush angrily responded Friday afternoon, calling the comment "pathetic."
"How pathetic for @realdonaldtrump to criticize the president for 9/11. We were attacked & my brother kept us safe," he tweeted.
On Friday evening after the rally, Trump took to Twitter to double down on the comment, saying he had merely been polite when Bush defended his brother during the most recent Republican debate.
"At the debate you said your brother kept us safe- I wanted to be nice & did not mention the WTC came down during his watch, 9/11," he tweeted.
Trump wasn't finished.
"No @JebBush, you're pathetic for saying nothing happened during your brother's term when the World Trade Center was attacked and came down," Trump tweeted about 20 minutes later.
He soon added: ".@JebBush, like it or not, our country needs more energy and spirit than you can provide! #MakeAmericaGreatAgain"
Bush's White House Press Secretary, Ari Fleischer, told CNN Friday that Trump sounds like a "truther," slang for someone who believes the U.S. government was behind the attacks.
"When Donald Trump implies that since 9/11 took place on Bush's watch he is partially responsible for it, he's starting to sound like a truther," he said. "And after all, does Donald Trump also think since Pearl Harbor happened on FDR's watch that FDR is responsible?"
"I just think he belongs to an extraordinarily small faction of people who blame 9/11 on George Bush. Interestingly, Hillary Clinton was one of those people for short time," he added.
Appearing in suburban Washington on Friday evening, Trump's presidential rival Ben Carson distanced himself from Trump's remark -- though he said he hadn't heard it.
"I would be surprised if he blamed him for it. That wouldn't make much sense, would it?" he said. "I think it's ridiculous to suggest that he's responsible for it."
Trump has previously taken aim at Bush, calling his presidency a "disaster." And he said last week that the decision to invade Afghanistan in 2001 was a "terrible mistake."
"We made a terrible mistake getting involved there in the first place," Trump said. "It's a mess, it's a mess and at this point we probably have to (leave U.S. troops in Afghanistan) because that thing will collapse in about two seconds after they leave."
Trump's comments to Bloomberg on Friday came in response to a question from Ruhle about his "soft hand." She said the world had seen his strong side, but Bush after 9/11 and President Barack Obama after the Sandy Hook massacre both had to stand in front of America and show a different side of them.
"I need to know that you will make us feel safe and you will make us feel proud," Ruhle said to Trump.
"I think I have a bigger heart than all of them. I think I'm much more competent than all of them," Trump said, before getting into the criticism of Bush.
He didn't spare Obama -- though he did not seem to lay the blame for the school shooting at his feet in the same way as Bush.
"If you look at Sandy Hook, those people are still begging for help. It's a disaster, and it's a disaster all over the place," Trump said.
"What we need is a leader. We don't have a leader," he added.
CNN's Jeremy Diamond and Theodore Schleifer contributed to this report.