MILWAUKEE, Wis. -- GOP candidates clashed Tuesday night over immigration and foreign policy in the fourth Republican presidential debate.
Kentucky Sen. Rand Paul lobbed the first attack of the night at Florida Sen. Marco Rubio by questioning his conservative credentials on taxes and military spending.
Pointing to Rubio's plans to expand the military by nearly $1 trillion while reducing sharply cutting taxes, Paul said, "Can you be a conservative -- and be liberal in military spending?"
Rubio fired right back: "I know that Rand is a committed isolationist. I'm not."
Paul also slammed Rubio's plan to expand the child tax credit, which Paul said amounts to a new expensive welfare program.
"We have to decide what is conservative and what isn't," Paul said.
Meanwhile, Ben Carson blasted the media. The political newcomer and retired neurosurgeon slammed journalists for what he characterized as lies about his past. Carson also said the press is treating Democratic front-runner Hillary Clinton more favorably.
"I have no problem with being vetted. What I do have a problem with is being lied about," Carson said.
He added: "When I look at somebody like Hillary Clinton, who sits there and tells her daughter and a government official that, 'No, this was a terrorist attack,' and then tells everybody else that it was a video, where I came from, they called that a lie."
His comments come after CNN reported last week that nine childhood friends, classmates and neighbors who grew up with Carson said they had no memory of the anger or violence the candidate has described.
The debate in Milwaukee, hosted by Fox Business, comes at a critical time in the 2016 race. Similar to retired neurosurgeon Ben Carson, Florida Sen. Marco Rubio is under scrutiny as his poll numbers rise. Critics of the Florida senator have seized on his use of a Florida Republican Party charge card for personal use.
Meanwhile, the struggles of Jeb Bush -- once viewed as the party's eventual front-runner but now stuck in the single digits -- have created an opening that his peers are jockeying to fill.
Though the event lacked some of the fireworks of previous debates, it did expose disagreements on immigration and foreign policy.
Former Florida Gov. Jeb Bush and Donald Trump butted heads on national security, disagreeing on the role for the U.S. in confronting the rise of ISIS.
"We can't continue to be the policemen of the world," said Trump, who has argued that the U.S. should let Russia take the lead in fighting ISIS in Syria.
Bush, who has faced criticism for failing to command previous debate stages, quickly shot back.
"Donald is wrong on this," Bush said. "We are not going to be the world's policemen, but we sure as heck better be the world's leader."
Carson, meanwhile, struggled when asked to address U.S. presence in Syria, offering a meandering answer.
"Putting the special ops people in there is better than not having them there," he said about President Barack Obama's decision to send 50 special operations forces to fight ISIS in Syria. "They're actually able to guide some of the other things that we're doing there."
The controversial issue of immigration reform pitted those with more moderate views such as Bush and Ohio Gov. John Kasich against immigration hardliners such as Texas Sen. Ted Cruz.
Bush argued that mass deportation of undocumented people currently in the United States is "just not possible and it's not embracing American values."
"It would tear communities apart and it would send a signal that we're not the kind of country America is," he said.
Cruz made the case that following the law is not the same thing as lacking in compassion.
"Every sovereign nation secures its borders and it is not compassionate to say we're not going to enforce the laws and we're going to drive down the wages for millions of hard-working American workers," the senator said.
Rubio, who had a standout debate performance last month in Boulder, Colorado, kicked off the prime-time showdown by arguing against raising the minimum wage -- a popular view among Republicans -- and pointing to the success of his own parents despite their humble backgrounds.
"If you raise the minimum wage, you're going to make people more expensive than a machine," he said.
Both Trump and Carson appeared to go one step further, saying wages in general were too high.
Carson, the only African-American presidential candidate this cycle, said "high wages" were at least partly to blame for high unemployment among black people.
Trump argued that wages were "too high," and that raising the minimum wage would hurt economic growth.
Rubio also pressed for stronger vocational training, again seizing a moment to present himself as an advocate for the middle class.
"We need more welders and less philosophers."
Cruz stumbled in listing his plans to eliminate five federal agencies.
Cruz identified "five major agencies that I would eliminate: the IRS, the Department of Commerce, the Department of Energy, the Department of Commerce and HUD."
Cruz listed the Department of Commerce twice. According to his website, the plan also includes the Department of Education.
The moment was reminiscent of a Republican debate in 2011, when former Texas Gov. Rick Perry failed to remember one of three federal agencies he pledged to eliminate, saying, "Oops."
Carson, Trump, Rubio, Cruz, Kasich and Bush were joined by Carly Fiorina and Rand Paul for the prime-time showdown.
Four lower-tier candidates --- Chris Christie, Mike Huckabee, Bobby Jindal and Rick Santorum --- kicked off the evening with a one-hour "undercard" debate. Christie and Huckabee had qualified for the main debates in previous gatherings.
Christie, known for his bold style, used the earlier debate to repeatedly slam Clinton -- part of a strategy to make the case that he could take on the Democratic front-runner during a general election.
"If you listen to Hillary Clinton," Christie said, "she believes that she can make decisions for you better than you can make them for yourself."
The New Jersey governor, whose political fortunes have fallen drastically following the state scandal dubbed "Bridgegate," also called on Republicans to train their fire on Clinton rather than each other.
"She is the real adversary tonight, and we better stay focused as Republicans on her," he said. "Hillary Clinton's coming for your wallet, everybody. Don't worry about Huckabee or Jindal, worry about her."
Jindal made a contrasting case, insisting that not just any Republican was capable of taking on Clinton.
"Let's not just beat Hillary -- let's elect a conservative," Jindal said, before going after Christie for his record in New Jersey. "Records matter."
Tempers flared at the media when a moderator asked each of the candidates to name a Democratic member of Congress they admire the most.
"I think this is why people were so frustrated with the last debate, with these kinds of silly questions," Jindal shot back, adding that he would fire everyone in Washington as president.
The other three candidates declined to engage the question, offering up unrelated answers.
Lindsey Graham and George Pataki did not qualify for either debate.