Republican presidential candidates expressed support for strengthening U.S. borders as they debated Tuesday night on immigration, the economy and the country's place in the world, but had different opinions about what to do with the millions of illegal immigrants already living in the country.
Billionaire Donald Trump, who was virtually tied with neurosurgeon Ben Carson in a new poll released before the debate, said the U.S. has no choice but to deport them.
"We are a country of laws," Trump said. "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, ask Israel."
Texas Senator Ted Cruz said it is possible for the U.S. to embrace legal immigration while also enforcing the rule of law, and that "every sovereign nation secures its borders."
Jeb Bush, left, speaks as Marco Rubio listens during Republican presidential debate at Milwaukee Theatre, Tuesday, Nov. 10, 2015, in Milwaukee.
But others in the field disagreed, led by Ohio Governor John Kasich, who said any plan to deport the 11 million illegal immigrants currently in the U.S. is "silly." He advocated a system in which those who are law abiding can pay a penalty to stay.
Former Florida Governor Jeb Bush said deporting illegal immigrants would "tear families apart," advocated allowing people to earn legal status over time.
Trump expressed support for Russia's military actions in Syria while questioning the aid being sent to moderate rebels. He said the U.S. cannot be the world's policeman.
Bush, who along with Kasich and businesswoman Carly Fiorina called for a no-fly zone in Syria, said America needs to be a leader and that it is "tragic" Iraq and others are talking to Russia.
"We are not going to be the world's police, but we sure as heck better be the world's leader," Bush said.
Fiorina called for rebuilding missile defense systems in Poland, carrying out military exercises in the Baltic, and adding thousands more troops in Germany to send a message to Russian President Vladimir Putin that the U.S. stands with its allies.
Kasich endorsed providing arms for people in Ukraine to "fight for themselves."
On China, Kasich said he would respond to cyberattacks by destroying the mechanisms used to break into computer systems. He also praised President Barack Obama for sending a U.S. ship to sail in the waters near the Spratly islands in the South China Sea, an area he said China does not own.
FILE - The aircraft carrier USS Theodore Roosevelt (CVN 71) transits the South China Sea in this U.S. Navy picture taken Oct. 29, 2015. U.S. Secretary of Defense Ash Carter will visit the Roosevelt as it transits the South China Sea on Thursday.
David Canon, a political science professor at the University of Wisconsin, said Kasich's answer on foreign policy was the best among the candidates.
"As someone with extensive experience in Washington, Kasich I think distinguished himself as quite knowledgeable on foreign policy, something he had not really talked about that much in previous debates," Canon said.
One of the most heated exchanges in the debate came as Kentucky Senator Rand Paul questioned Florida Senator Marco Rubio on the defense budget, saying it is not possible to be a conservative while being liberal on military spending.
"I know the world is a safer and better place when America is the strongest military power in the world," Rubio shot back.
Canon said the debate featured more "ganging up" on Obama and Democratic presidential candidate Hillary Clinton than in prior events, but that the discussion between Rubio and Paul pointed out the differences among the Republicans as the field begins to thin.
"That was the most pointed exchange of the night that gets to [the] point that someone has to stand out now as who the Republican is we're supposed to back here, not just 'we have to beat Hillary Clinton,' " he said.
Carly Fiorina, center, speaks as Ted Cruz, left, and Rand Paul, right, listen during a Republican presidential debate at Milwaukee Theatre, in Milwaukee, Nov. 10, 2015.
Trump said the U.S. needs to make its military "bigger, better and stronger" than ever before. He also supported all of the Republican tax plans over what he called "the mess" in place now.
A new McClatchy/Marist poll, released just before the debates, showed Carson leading with 24 percent and Trump just behind at 23 percent. Rubio was a distant third with 12 percent, while Cruz and Bush were tied for fourth at 8 percent.
But Canon said the front-runners Trump and Carson were the flattest performers who hurt themselves the most Tuesday night.
"Trump said virtually nothing in his closing statement at all and Ben Carson talking about drug addicts dying and abortions, you don't want a downer message like that for your closing statement," he said. "You want to have something more uplifting and looking to the future, more like Rubio's statement or Ted Cruz or Carly Fiorina."
Two other candidates -- New Jersey Governor Chris Christie and former Arkansas Governor Mike Huckabee -- were demoted after the first three debates to the so-called "undercard debate" held earlier in the evening.
It also featured former Pennsylvania Senator Rick Santorum and Louisiana Governor Bobby Jindal.
All four took the opportunity early in their session to promote plans they claim will make the U.S. tax code fairer. Huckabee proposed getting rid of the Internal Revenue Service, which is responsible for tax collection and tax law enforcement.
Bobby Jindal, left, Chris Christie, Mike Huckabee and Rick Santorum talk to moderators Trish Regan, Gerald Seib and Sandra Smith, right, after a Republican presidential debate at Milwaukee Theatre, in Milwaukee, Nov. 10, 2015.
Christie and Santorum shared their distaste for the Federal Reserve -- the nation's central bank. The two claimed that the Fed has kept interest rates artificially low to support President Obama.
Trump made similar claims recently.
At the time, White House spokesman Josh Earnest insisted the Fed acts independently, saying the administration "goes to great lengths" to ensure that the Fed can make decisions solely on the economy's interests and to prevent those decisions from being influenced by politics.
Christie, trying to have a breakout night after being taken off the main stage following the first three debates, focused much of his attention during the evening on Democratic front-runner Clinton, whom he called "the real enemy. [She's] coming for your wallet, everybody. Don't worry about Huckabee or Jindal, worry about her."
Christie's jab at Clinton followed a back-and-forth argument between Jindal and Huckabee over their records as governors.
Looking straight into the camera, Christie said, "If you think Mike Huckabee won't be the kind of president who will cut back spending, or Chris Christie, or John Kasich, wait till you see what Hillary Clinton will do to this country. She will drown us in debt. She is the real adversary tonight."