The former Florida governor criss-crossed the first-in-the-nation primary state of New Hampshire, where he repeatedly went after Trump in his stump speeches -- unprompted -- and in conversations with voters.
In his first of four town halls Saturday morning, he uttered perhaps his strongest comments yet about the Republican presidential front-runner.
"Just one other thing -- I gotta get this off my chest -- Donald Trump is a jerk," Bush said to laughter and applause at his town hall Contoocook, New Hampshire.
The outburst came after a man who said he had Asperger's Syndrome asked Bush how he would help people with disabilities as president.
Bush talked about the work he did in Florida with the state legislature to obtain more money for the state's disability system. Just when it appeared he was done with his answer, Bush started his rant against his GOP rival.
"You cannot insult your way to the presidency," he said, reiterating an attack line he's been firing at Trump. "You can't disparage women, Hispanics, disabled people. Who is he kidding?"
Trump took on widespread criticism when he appeared to mock a New York Times reporter with a disability
last month, though Trump denied he was doing so.
The two candidates had been sparring all week after Bush started executing a new strategy of directly confronting Trump at the CNN debate in Las Vegas on Tuesday. They continued trading shots throughout the week, with Trump calling Bush "dumb as a rock"
on Twitter Friday and getting in some fresh insults Saturday while campaigning in Iowa.
Continuing to dig in, Bush said in Contoocook that it's "deeply discouraging" that Trump is "actually running for president and insulting people."
"We should reject that out of hand. And I hope you're going to reject it by voting for me," he told the audience. "But a guy like that should not be the front-running candidate of our great party. That is not how we win."
After more applause, Bush added: "I feel better now. I gave myself therapy there. Thank you for allowing me to do it."
Voters at Bush's town halls were largely receptive to his digs at Trump. At one point, in Exeter, a voter asked Bush how Trump could be defeated.
"First of all, do you want me to?" Bush asked, as the audience of a little more than 200 erupted in cheers and applause, with some people shouting "Yes!"
In Windham, a voter asked Bush if he thought Trump would lose the general election by a "landslide."
"Beyond question, Trump loses to Hillary Clinton," Bush said. "Beyond question."
Along with calling him a "jerk," Bush needled Trump over not knowing about the nuclear triad, quipping that Trump probably thought it was "like a tripod." He thrice spotlighted Trump's love-fest with Putin, found a way to work in a Trump critique in a point about the space program, and even questioned Trump's "intellectual curiosity" on more than one occasion.
"I don't think Donald Trump knows the Kurdish people are Muslim. That wouldn't be one of those things that naturally comes to him," Bush said, when talking about Trump's proposal to ban non-U.S. Muslims from coming into the country. "He doesn't have much intellectual curiosity. It means the Kurds we're asking to fight the fight (against ISIS) wouldn't be allowed to come into the country."
Bush's jabs came the same day that the super PAC supporting his White House bid, Right to Rise, released a new TV ad hitting Trump.
The ad is almost identical to a web video released by the campaign earlier this week spotlighting Bush's attacks in the debate against Trump over past statements that he's made.
Later Saturday, Trump continued his attacks on Bush during a campaign rally in Cedar Rapids, Iowa, calling him "incompetent" and "terrible."
"It was so sad to watch him (at Tuesday's debate)," he said.
Trump later said he's not looking for Bush's approval.
"I don't want Jeb Bush's endorsement. It doesn't mean anything. He's not tough. He's not smart," he said. "I want endorsements from the absolute best."
For Bush on Saturday, it all boiled down to one point that he wanted to get across. With Trump sitting comfortably at the top of the polls in New Hampshire, he urged voters to seriously consider the power of their vote, saying they can determine "the fate of Donald Trump" and expressed confidence that they'll "do the right thing."
Bonnie Sanders, a voter from Windham who attended Bush's town hall, said a potential nomination for Trump is one of her biggest concerns. "What's our best hope of Trump not being on the ticket?" she asked, adding that she liked that Bush went after the front-runner but wasn't sure that he'd be the one to finally knock Trump out of the running.
Debbie Robinson, also from Windham, said Bush's offensive against Trump at the debate was "good" and that Trump "had it coming," but suggested he temper his attacks and not go after Trump "all the time."
And if Trump becomes the nominee? Both women said they'd write somebody in. "Maybe Jeb," Robinson said.