Trump battles Jeb Bush, other Republicans at debate
Jeb Bush speaks to Fox News (screen grab)

Republican front-runner Donald Trump came under early fire from former Florida Governor Jeb Bush and other presidential rivals in a debate on Wednesday, but Trump brushed off the attacks and said he had the right temperament to be president.

Trump, who has shot to a big lead in the 16-strong 2016 Republican presidential race, touted his business experience and said it was the main thing drawing Republicans to his candidacy.

A frequent target of Trump's jibes for his "low-energy" campaign, Bush criticized Trump for his past friendliness with Democrats such as House Democratic Leader Nancy Pelosi, New York Senator Chuck Schumer and former President Bill Clinton, and for trying to get involved in casino gambling in Florida.

"He supports Pelosi, he supports Schumer, he supports Clinton. And he asked Florida to have casino gambling and we said no," Bush said.

Trump shrugged his shoulders dismissively and denied trying to get into the casino industry in Florida. "Wrong... Jeb, come on." He added: "More energy tonight? I like that."

Bush, an establishment Republican, has been overshadowed by Trump's bomb-throwing rhetoric in the contest to become the party's candidate for the November 2016 presidential election but promised to be more aggressive.

Trump fired off another attack at U.S. Senator Rand Paul of Kentucky, saying he did not even belong on the stage, but Paul criticized Trump for his "sophomoric" criticisms of people's appearance.

"I never attacked him on his looks, and believe me there's plenty of material there," Trump said.

Reuters/Ipsos opinion polling shows Trump leading among Republicans with 32 percent. Retired neurosurgeon Ben Carson is second at 15 percent. Bush, the younger brother of former President George W. Bush, is in third place at 9 percent as his campaign struggles to take off.

Eleven candidates were on stage for the debate at the Ronald Reagan Presidential Library in Simi Valley.

It is the first time Trump has been on stage with former Hewlett-Packard Chief Executive Carly Fiorina, whom he insulted in recent weeks with a comment about her face.

Also debating in the main event are Scott Walker, Ted Cruz, Marco Rubio, Mike Huckabee, Rand Paul, John Kasich and Chris Christie.

Before the prime-time encounter, Rick Santorum, Bobby Jindal, George Pataki and Lindsey Graham participated in the "undercard" debate for those candidates who did not poll strongly enough to qualify for the main event.

Jindal, the Louisiana governor, and Pataki, the former New York governor, led the early charge against Trump.

"Let's stop treating Donald Trump like a Republican," said Jindal. "He's not a conservative. He's not a liberal. He's not a Democrat. He's not a Republican. He's not an independent. He believes in Donald Trump."

Pataki, who has vowed not to support Trump if he is the nominee, insisted Trump would not get that far.

"Donald Trump is not going to be the Republican nominee, period. I guarantee you that," Pataki said.