Carly Fiorina, a former HP executive, appeared set to gain from the debate as a fellow political outsider by frequently going after Trump directly and addressing specific foreign policy challenges to highlight his lack of depth.
Trump dismissed efforts to pin him down on foreign policy specifics pointing to his persona and experience with international business deals as ways to smooth out international crises.
"I will get along, I think, with Putin, and I will get along with others, and we will have a much more stable world," he said.
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Fiorina scoffed at the idea, calling Puting a "bad actor" that the US should isolate.
It also got personal between the two as they attacked each other's business records and Fiorina responded to earlier comments by Trump about her looks.
Jeb Bush, once considered the likely frontrunner, lags far behind, tied in a distant third in the CBS/New York Times poll with support from just 6% of Republican primary voters.
He sought to reclaim the mantle of the party once led by his father and brother, but was forced to share the stage with the political outsiders that have dominated the campaign so far.
Inflammatory remarks
"You can't just, you know, talk about this stuff and insult leaders around the world and expect a good result," he said, alluding to Trump's brash style. "You have to do this with a steady hand, and I believe I have those skills."
Bush was also forced to defend his family ties as a son and brother of the last two Republican presidents and took Trump to task for attacking his Mexican wife.
"I'm my own man. I'm going to create a strategy that is based on the simple fact that the United States needs to lead the world," he said, noting the next president would take office in 2017, not 30 or 16 years ago when presidents George HW Bush and George W Bush took office.
Concern within the Republican Party has grown as Trump has continued to rise despite inflammatory remarks that many fear could damage the centre-right party's brand ahead of November 2016 general elections.
Trump caused waves in the first debate last month when he refused to rule out running for president as a third party candidate – a move that would surely hurt Republican chances of recapturing the White House. He has since signed a pledge vowing to support the party's nominee.
The first ballots will not be cast in intra-party primaries until February, in a series of state-by-state contests with the nominees from the Republican and Democratic parties facing off in November 2016. – DPA
