Standing in front of President Reagan's Air Force One in his presidential library in California, the candidates came into clearer focus for voters.

As the Republican leading in the polls, Donald Trump took center stage.

"I wrote, The Art of the Deal. I say this not boasting, but I've made billions and billions," he said in his opening statement.

New to the top tier debate stage was Carly Fiorina, who didn't miss a chance to spar with Trump.

When asked about Trump's remarks about her face, Fiorina said, "Women all over this country heard very clearly what Mr. Trump said."

Early in the debate Fiorina took opportunities to show off her knowledge of foreign policy, but her most passionate response came while answering a question about federal funding for Planned Parenthood.

"This is about the character of our nation and if we will not stand up and force President Obama to veto this (budget) bill, shame on us," she said.

The two men following Trump in the polls stood to his right and left.

Dr. Ben Carson won "gotcha" points with Trump during a discussion about vaccinations and autism. (Screengrab via CNN.com)

Carson says vaccines don't cause autism, but suggested there may be a number of vaccines that aren't necessary.

Trump believes vaccines are connected to autism. Carson doesn't, saying research doesn't show that to be true.

When asked about Trump's medical opinion, Carson grinned and said, "He's an okay doctor."

Standing on the other side of Trump, former Florida Gov. Jeb Bush worked to paint himself as a proven conservative leader.

On immigration, Bush asked Trump to apologize for bringing his Mexican born wife, Columba, into the debate. Trump said he hears Columba is lovely but refused to apologize.

When Bush's political pedigree was called into question, Trump accused former President George W. Bush of being such a bad president that he ushered in President Obama.

"There's one thing I know about my brother, he kept us safe," Bush replied, drawing major applause from the audience.

Over the three-hour top tier debate, CNN's moderators covered a lot of ground, from the legalization of marijuana to the Secret Service code names the candidates would choose if they're elected.

With such a crowded field, candidates are desperately working to carve out their niche and climb to the top of the pack.

Texas Sen. Ted Cruz was passionate in his opposition to the Iran nuclear deal, calling it catastrophic.

"There is no more important topic in 2016," he said.

Former Arkansas Gov. Mike Huckabee chimed in saying, "President Obama treats the Iran nuclear deal like the Magna Carta while Iran uses it as toilet paper."

Fresh from his public support of Kentucky clerk Kim Davis, Huckabee spent time talking about religious liberty.

"We made accommodations for the Fort Hood shooter to grow a beard ... are you telling me we can't accommodate an elected clerk in Kentucky?" he asked.

Wisconsin Gov. Scott Walker, looking to make up recent slips in the polls, took a jab at front-runner Trump.

"We don't need another apprentice in the White House; we have one there now," Walker said, playing off of Trump's former TV show.

"Now more than ever America needs a leader who will go big and go bold again and I've been tested," Walker said. (Screengrab via CNN.com)

When asked about balancing Second Amendment rights to bear arms with efforts to curb gun violence, Florida Sen. Marco said, "Criminals ignore the law, you can pass all the gun laws in the world but criminals won't follow them."

New Jersey Gov. Chris Christie showed a slightly softer side than voters are used to seeing. He shared how difficult it was for him on September 11, 2001, not knowing for hours if his wife was okay as she worked at the World Trade Center.

He says going into Afghanistan after the attacks was the right thing to do.

He also thinks the nation needs to do a better job keeping tabs on the people who come into the country.

"We need to take the fingerprint of every person who comes here on a visa and track them down when they overstay," he said.

In a clear effort to appeal to the Republican Party base, Ohio Gov. John Kasich painted himself as a conservative willing to bring parties together and get things done.

You have to be able to "land the plane," he said, pointing to Reagan's Air Force One behind him.

Kentucky Sen. Rand Paul explained his plan to eliminate the entire tax code and replace it with a 14.5 percent tax on everyone.

He says it's important for America to talk to her enemies like Reagan talked to the Soviet Union during the Cold War, but he's not a fan of more American boots on the ground in the Middle East.

"I'm not sending our sons and daughters back to Iraq," Paul said. "The Kurds deserve to be armed and I'll arm them."

Before the three-hour debate between the top tier candidates, four of the second tier candidates debated on the same stage.

South Carolina Sen. Lindsey Graham brought his best humor and also took every opportunity to bring up radical Islam while promoting his foreign policy credentials as a member of the U.S. Senate.

"I have a plan to defeat radical Islam," he said in his final statement adding, "These are radical Nazis running wild."

Louisiana Gov. Bobby Jindal worked to paint himself as an outsider willing to shake up Washington, DC. He also took on Trump right out of the gate.

"Let's stop treating Donald Trump like a Republican," Jindal said.

Former Sen. Rick Santorum said attacking each other only helps Democrat Hillary Clinton. He worked hard to appeal to evangelical voters and by extension caucus goers in Iowa. It's a state Santorum won last cycle, but this time around he's had a hard time moving his poll numbers.

"We need a president to fight a Supreme Court that has been abusive," Santorum said.

Former New York Gov. George Pataki walked a fine line between strong national defense and appealing to the base of the Republican Party. He won the governor's mansion in one of the most liberal states in America running as a conservative. Pataki says that makes him a strong contender to win the general election.

"I can win and govern successfully," Pataki said.

One advantage of being in the 2nd tier debate is the candidates got more questions and more opportunities to distinguish themselves from the pack.

The big question after the 2nd debates will be answered in time, which candidate will get a boost in the polls?

Click here to watch interviews with various candidates.

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