(CNN)Responding to a volley of critical tweets and comments from Jeb Bush, Donald Trump on Monday called his rival -- the son of one president and brother of another -- an "embarrassment to his family."
Donald Trump: Jeb Bush is an 'embarrassment to his family'
Moments earlier, Bush told CNN's Dana Bash he was a "joyful warrior," who wouldn't sit back and watch "someone try to hijack a party that I believe will allow people to rise up again."
Trump, who had been watching Bush's interview, fired back immediately, launching a series of aggressive attacks and insults at the former Florida governor.
"Jeb is having some kind of a breakdown," he told CNN's Wolf Blitzer. "He's an embarrassment to his family. He has to bring his mother out and walk his mother around at 90 years old. I think it's a very sad situation that's taking place."
"Frankly, he's a stiff," Trump said. "He's not a guy who can be president. He doesn't have what it takes to be president."
Barbara Bush, Jeb's mother, recently joined her son on the campaign trail in New Hampshire, where the former first lady ripped Trump, saying she was "sick of him" and "not crazy about what he says about women."
Trump, though, kept his focus trained on Jeb Bush.
"He's a desperate person. He's a sad and a pathetic person. He doesn't even use his last name in his ad," Trump said, asked to react to a tweet Bush's campaign sent out earlier calling him a "loser" and a "liar." "He's a sad person who has gone absolutely crazy. I mean, this guy is a nervous wreck."
The billionaire also swatted away Bush's claim to being the only GOP candidate willing to stand toe-to-toe with Trump on the debate stage.
"[Bush] goes around saying, 'I'm the only one with the courage to go after Trump.' What courage is it?," Trump asked. "He says nasty things and I put him down on the dais and he goes away like a little sheep."
Trump also dismissed Bush's assertions that, despite their primary fight, he and former colleague and protege Marco Rubio were still "friends."
"He hates Rubio so much, he can't stand the sight of him," Trump said, adding that Bush believes Rubio "violated the friendship" by deciding to run for the Republican nomination.