MILWAUKEE (AP) — A feisty Jeb Bush sought to regain his footing in Tuesday's Republican presidential debate, challenging President Barack Obama's economic record and criticizing Democratic front-runner Hillary Rodham Clinton for pledging to build on his policies.

"It may be the best Hillary Clinton can do, but it's not the best America can do," said Bush, who is attempting a campaign reset after a sluggish start to his bid for the GOP nomination.

The debate opened with a narrow focus on economic policy, with moderators from Fox Business News allowing the candidates to deliver lengthy answers. There was little interaction among the candidates at first, and the moderators didn't attempt to get them to engage each other, a notable shift after Republicans criticized the aggressiveness of the hosts in the last debate.

That didn't last, though. Billionaire businessman Donald Trump and Ohio Gov. John Kasich went after each other aggressively when the subject of immigration came up — Trump insisting anew that 11 million or more immigrants in the country illegally be removed — and Florida Gov. Bush chimed in as well.

Retired neurosurgeon Ben Carson entered the debate facing questions about the veracity of his celebrated biography, which has been at the center of his connection with voters. Carson pushed back on the questions and suggested the media were harder on him than Clinton.

"We should vet all candidates," Carson said. "I have no problem with being vetted. What I do have a problem with is being lied about."

While pieces of Carson's background had been challenged earlier in the campaign, the questions ballooned last week after CNN reported it could not find friends or confidants to corroborate the story, told in his widely read autobiography, of his unsuccessfully trying to stab a close friend when he was a teenager.

The debate, the last for the GOP until mid-December, could help shape the course of the campaign into the winter as voters begin to pay more attention to the White House race.

Drawing a sharp contrast with Democrats, the candidates voiced opposition to raising the federal minimum wage, casting it as an impediment to job growth.

"If you raise the minimum you're going to make people more expensive than a machine," Florida Sen. Marco Rubio said.

Trump concurred. "We cannot do this if we're going to compete with the rest of the world," he said.

Democratic front-runner Clinton has called for raising the minimum wage from $7.25 an hour to $12. Her chief rival, Vermont Sen. Bernie Sanders, has backed an increase to $15.

Trump has led the field for months, defying standard political logic, while experienced governors and senators have struggled to break through. Carson, another outsider, has begun challenging Trump's hold on the GOP contest.

The debate could be crucial for Bush. The former Florida governor has sought to interject early, reminding moderators that he had limited time in the last contest two weeks ago.

"I got about four minutes in the last debate," Bush said.