Republican presidential candidates Marco Rubio (L) and Donald Trump confer during a break in the Republican Presidential Debate November 10, 2015 in Milwaukee, Wisconsin
Milwaukee (AFP) - Republican White House hopefuls struggled to break away from the pack in an election debate with fewer personal barbs, but some feisty exchanges on immigration and national security.
Eight top candidates gathered in Milwaukee, Wisconsin for a forum that distilled differences between candidates in substance and style, but did little to dramatically change the contours of the race.
Retired neurosurgeon Ben Carson and billionaire real estate mogul Donald Trump entered the evening leading the race to become the Republican nominee in the November 2016 contest to succeed President Barack Obama.
But it was their establishment rivals who took the lead in the debate, hoping to punch through with a command of economic policy and by training the focus on Obama and likely Democratic candidate Hillary Clinton.
Former Hewlett-Packard chief executive Carly Fiorina, offered some of the sharpest criticism of the Democratic frontrunner.
"A Clinton presidency will corrode the character of this nation. Why? Because of the Clinton way. Say whatever you have to, lie as long as you can get away with it," Fiorina said.
Coming into the forum fighting for his political life, one-time favorite Jeb Bush -- the sometimes avuncular son of the 41st president and brother of the 43rd president -- sought to break through with some tougher talk.
"Hillary Clinton has said that Barack Obama's policies get an 'A' -- really?" Bush asked derisively, listing woes ranging from a discouraged work force to high poverty levels, to kids on food stamps.
That "may be the best that Hillary Clinton can do but it is not the best America can do."
- 'We will have a wall' -
Bush took the debate to Trump by trashing his immigration plan as unworkable and unpatriotic.
Addressing proposals to repatriate 12 million illegal immigrants, Bush said: "500,000 a month is just not possible, and it's not embracing American values and it would tear communities apart."
Trump hit back by saying: "We need borders. We will have a wall. The wall will be built. The wall will be successful. And if you think walls don't work, all you have to do is ask Israel."
Flagging poll numbers and poor debate performances have spooked Bush's supporters, as well as crucial big money donors, who once fawned over the former Florida governor.
"I know I have to get better," Bush told supporters last week after his lackluster performance in the previous debate.
It remains to be seen if he did enough Tuesday to retain the crown of establishment Republicans against a tough challenge from one-time political protege Marco Rubio, who again turned in a polished and disciplined performance.
He won applause for a spirited rejection of rival Rand Paul's call for a more modest national security policy, with military spending to match.
"I know that the world is a safer and better place when America is the strongest military power," said Rubio.
- Out with the 'gotcha' -
But Tuesday's Republican debate saw little of the fractious infighting that has marked the Republican campaign so far.
The previous debate, hosted by cable business channel CNBC, was defined by the confrontational tone that moderators took with the candidates, many of whom complained about being asked "gotcha" questions.
Carson, a retired neurosurgeon who has stumbled in recent days amid questions about the veracity of his inspirational personal narrative, largely avoided scrutiny.
"Thank you for not asking me what I said in the 10th grade. I appreciate that," Carson, the only African-American in the field, told moderators.
His accounts of receiving an offer of a prestigious military scholarship and his violent adolescence, when he says he attempted to stab a classmate, have come into question.
"I have no problem with being vetted. What I do have a problem with is being lied about," he said.
Amid pressure to narrow the field for Tuesday's debate, which initially focused on the economy, broadcaster Fox Business Network changed the format, with only eight candidates at the podiums instead of 10.
Senator Ted Cruz and Ohio Governor John Kasich rounded out the main debate field.
Low-pollers Chris Christie and Mike Huckabee however failed to make the cut. They were relegated to an undercard debate that was held prior to the main event and which also featured Louisiana Governor Bobby Jindal and former senator Rick Santorum.
Christie made a strong case for himself getting back on the main stage, arguing that Republicans ought to stop attacking one another and focus their efforts on preventing Clinton from expanding government.
"She is the real adversary and we'd better stay focused on... her," he said.
"Hillary Clinton's coming for your wallet, everybody. Don't worry about Huckabee or Jindal, worry about her."