BOULDER, Colo. (CBSNewYork/AP) — Ben Carson entered Wednesday night’s third GOP presidential debate with a surge of momentum — and quickly found himself in the crosshairs of rivals along with longtime frontrunner Donald Trump.

As CBS2 Political Reporter Marcia Kramer reported, the Republican debate Wednesday night at the University of Colorado Boulder was the first for which Trump was not atop the leaderboard. Trump has fallen behind Carson in the Iowa polls, and the latest national CBS News/New York Times poll also showed Carson ahead of Trump.

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But both were the subject of barbs and bickering during the debate.

The first question for the candidates was about their biggest weakness. But Ohio Gov. John Kasich launched into an attack onto some of the leading candidates’ ideas instead.

“My great concern is that we are on the verge perhaps of picking someone who cannot do this job,” Kasich said.

Without naming anyone, he said he had heard talk about dismantling Medicare and Medicaid, deporting 10 million or 11 million people out of the country, and “tax schemes that don’t add up and put our kids in a deeper hole.”

For his part, Trump said: “I trust people too much. I’m too trusting. And when they let me down, if they let me down, I never forgive. I find it very, very hard to forgive people that deceive me.”

Carson said his weakness was not being able to see himself as a potential U.S. president until “hundreds of thousands of people began to tell me.”

A short time afterward, Carson faced a question on his flat tax plan – which CNBC moderator Becky Quick said was appealing to many voters, but would cut the total amount of revenue for the federal government — $1.5 trillion – to less than half of its current total.

Carson said the rate would be closer to 15 percent, and other problems would be dealt with by cuts.

But Kasich quickly dismissed the idea as “fantasy.”

“These plans would put us trillions and trillions of dollars in debt,” Kasich said. He said he was the only candidate that had been involved in balancing the federal budget, and said he had a plan to do so while cutting taxes and creating jobs.

“I can get it done because I’m realistic,” Kasich said.

Trump in turn took aim at Kasich, pointing out that Kasich had been a managing general partner when Lehman Brothers went down. He further accused Kasich of changing his tone from being “nice” to “nasty” over the course of the campaign.

“His poll numbers tanked… and he got nasty,” Trump said.

Kasich said he was not on the board of Lehman Brothers, but was a banker who knew how to create jobs.

Trump once again defended his plan to demand that Mexico pay for a border wall. He also said he has a permit to carry a gun in New York, and said more people need to follow his lead.

He calls gun-free zones a “catastrophe,” describing them as “target practice for sickos and the mentally ill.”

Trump said he carries a gun on occasion, but adds, “I like to be unpredictable.”

Told that some Trump resorts and properties don’t allow guns, Trump says he’d consider a new policy. “I would change it,” he said

Trump summed up his message for the night as: “Our country doesn’t win anymore. We used to win. We don’t win anymore.”

Meanwhile, Carson pushed back on questions about his involvement with a medical supplement company that has come under legal scrutiny.

He said he made a few paid speeches for Texas-based Mannatech Inc. and uses its products, but calls it “absurd” to say he has a relationship with them.

Asked why his picture was on the home page for the company, Carson says they must have used it without his permission. When he was pushed over whether that betrayed any issues with his “vetting process,” the crowd began to boo.

Carson smiled. “They know,” he said.

Other candidates also traded their share of barbs. Florida Sen. Marco Rubio defended his job performance against criticism from one of his constituents — former Florida Gov. Jeb Bush.

Bush, once seen as the top Republican contender, quickly targeted Rubio for his spotty voting record on Capitol Hill — signaling that he sees the Florida senator as the candidate most likely to block his political path.

“Marco, when you signed up for this, this was a 6-year term and you should be showing up for work,” said Bush, who is struggling to right his campaign after being forced to slash spending in response to slower fundraising. “You can campaign, or just resign and let someone else take the job.”

Rubio, who has had a close relationship with Bush, responded sharply: “The only reason you’re doing it is that we’re running for the same position and someone has convinced you that attacking me will help you.”

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Rubio also turned later questions about his personal finances into an opportunity to tout his compelling personal story. The son of Cuban immigrants, Rubio said he didn’t inherit money from his family and knows what it’s like to struggle to pay loans and afford to raise a family.

“I know what it’s like to owe that money,” Rubio said. “I’m not worried about my finances. I’m worried about the finances of everyday Americans.”

Meanwhile, Bush dodged a question he had no problem answering four years ago: Would you sign a budget deal that cut $10 for every $1 in taxes raised?

He said, “Well, the deal was done.”

Bush added: “Now we see Hillary Clinton proposing a third term of economic policy for our country. We need to reverse that. And my record was one of cutting taxes each and every year.”

But Bush is not saying he would sign the deal today, when he’s a candidate for president, trying to gain traction.

Sticking with his attack on Congress, he says: “You find me a Democrat that will cut spending $10 — heck, find me a Republican in Congress that would cut spending $1 — I’ll talk to him.”

Zeroing in on Democrats, Bush said: “You find a Democrat that’s for cutting spending $10? I’ll give him a warm kiss.”

For his part, Texas U.S. Sen. Ted Cruz slammed the moderators for their confrontational questions.

“If you look at the questions – ‘Donald Trump, are you a comic book villain?’ ‘Ben Carson, can you do math?’ ‘John Kasich, will you insult two people who are here?… How about talking about the substantive issues?” Cruz said in response to a question about the debt limit.

When moderators pointed out that the question was about the debt limit, Cruz tried to backpedal and answer the question, and said, “You don’t want to hear the answer” when the moderators elected to move on.

References to socialism were also heard from many candidates during the debate, with Cruz saying the Democratic contest between Sen. Bernie Sanders, former Secretary of State Hillary Rodham Clinton, and former Maryland Gov. Martin O’Malley.

Cruz called the Democratic debate – which also included since-withdrawn candidates Lincoln Chafee and Jim Webb, a contest “between the Bolsheviks and the Mensheviks.”

New Jersey Gov. Chris Christie’s first remarks attacked the Democrats.

“I see a socialist, an isolationist and a pessimist, and for the sake of me, I can’t figure out which one is which.”

Former technology executive Carly Fiorina says it is the “height of hypocrisy” for Clinton to talk about being the first woman president when “every single policy” she endorses is “demonstrably bad for women.”

Fiorina claimed 92 percent of the jobs lost during President Barack Obama’s first term belonged to women. Cruz said 3.7 million women went into poverty during Obama’s presidency.

Cruz said big government benefits the wealthy, lobbyists and giant corporations, and said he is fighting for Hispanics, women and single mothers.

Also on stage were former Arkansas Gov. Mike Huckabee and Kentucky Sen. Rand Paul.

Paul called for small government, and spoke against raising the debt ceiling.

“I want a government so small that the individual has a chance to thrive and prosper,” Paul said.

And toward the end of the debate, Huckabee came to Trump’s defense – even saying he had come to the debate in a Trump tie.

“Donald Trump would be a better president every day of the week, and twice on Sunday, rather than Hillary,” he said.

But the bickering tone of the debate left some viewers disappointed, including radio host Meghan McCain, the daughter of U.S. Sen. John McCain.

Taken together, the Republican field that remains crowded and unwieldy with less than 100 days until the Iowa caucuses. The political rookies appealing to voter anger with Washington have ceded no ground, and establishment politicians are still waiting for the race to turn their way — and increasingly wondering if it ever will.

The jumbled GOP race is a stark contrast to the Democratic field, where Clinton has strengthened her standing as the clear front-runner. Campaigning in New Hampshire Wednesday, she said the GOP debates are like a “reality TV show but the cast of characters are out of touch with actual reality.”

The debate in Colorado, an important general election battleground state, ran for two hours after the last affair went on for more than three.

The four lowest-polling candidates participated in an earlier undercard event: South Carolina Sen. Lindsay Graham, former Pennsylvania Sen. Rick Santorum, Louisiana Gov. Bobby Jindal and former New York Gov. George Pataki. None has gotten close to breaking into the upper tier of candidates.

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