Republican presidential candidates on Thursday held their last debates before Monday's Iowa caucuses — the first event in which voters actually make their choices for their parties' next presidential nominees.
Most of the candidates quickly addressed FOX News moderator Megyn Kelly’s request to address “the elephant not in the room” Thursday night: that front-runner Donald Trump was not participating in the debate.
"I'm a maniac and everyone on this stage is stupid, fat and ugly, and Ben, you're a terrible surgeon," Texas Senator Ted Cruz said to rival Ben Carson, a retired neurosurgeon, saying that he had now "gotten the Donald Trump portion of the program out of the way."
Florida Senator Marco Rubio said while the billionaire candidate is entertaining, Trump is not what the campaign is about. And former Florida Governor Jeb Bush, who has often been the target of Trump’s barbs, joked that he missed having the real estate mogul on the stage.
WATCH: Talking about the 'elephant not in the room'
But the rest of the candidates avoided mentioning Trump and quickly moved on to establish their credentials as president.
Because of the large number of candidates — 11 — host FOX News split the debates in Des Moines, Iowa, between the seven candidates leading polls and the four bringing up the rear.
Immigration issue
In the most heated exchanges of the night, moderator Kelly, using video clips of candidates’ previous statements, questioned several candidates regarding their seeming flip-flops on the immigration issue.
Rubio campaigned for the Senate in 2010 on a tough immigration stance, saying he would never support blanket amnesty. He later became part of a bipartisan group of senators called the “gang of eight,” who crafted a comprehensive immigration bill in 2013 that contained a pathway to citizenship. The bill passed in the Senate but failed in the House of Representatives.
In a testy exchange with Kelly, Rubio denied he had changed his position on immigration, easily one of the most contentious issues for the Republicans. “What I’ve always said is this issue needs to be solved,” he said.
He said while he’s not for deporting the millions of undocumented immigrants in the U.S. -- as Trump has suggested he would do -- “we’re not for handing out citizenship either.”
Bush attacked Rubio, saying the senator had sought his support as governor on legislation that would allow a pathway to citizenship. But "then he cut and run because it wasn't popular with conservatives," he chided.
Rubio fired back, saying Bush "used to support" a path to citizenship.
The former governor responded: "So did you, Marco."
Attacks on Cruz
Cruz also had to answer video clips that showed him saying he would support immigration reform legislation, if some of the amendments he had offered were approved.
He denied he had changed his stance, saying his amendments were not to fix all of the legislation's problems but to ensure undocumented immigrants in the U.S. couldn't gain legal status.
Cruz's reply brought attacks from both Paul and Rubio. They accused Cruz of claiming to be the only "true" conservative on the immigration issue, while Cruz accused Rubio of changing his stance on immigration to appeal to donors.
Fox, which partnered with Google for Thursday's debate, used questions from various Americans throughout the debate.
One such question came from Dulce Candy, an Iraq war veteran who was brought to this country from Mexico as a child.
Appearing via YouTube, Candy asked how immigrants should feel welcome in the United States, given the harsh rhetoric regarding immigrants and refugees by the party's candidates during the past few months.
Bush responded, saying Candy "deserves our respect," while Rubio, again calling for reforming the immigration system, told her, "we will always celebrate legal immigration."
WATCH: Candidates on national security:
National security
Google said its searches reflecting the question “Is America safe?” have increased 400 percent since 2008, leading to questions posed about national security.
Rubio and Kentucky Senator Rand Paul had a heated exchange over how far the government can go in anticipating domestic terrorism.
Rubio, warning the U.S. faces an unprecedented threat from the Islamic State group, said he would go after terrorists "wherever they are" and if caught, "we're sending them to Guantanamo," referring to the detention center for prisoners in Cuba.
He has called for shutting down mosques, which he said are being used to radicalize terrorists.
Paul called Rubio’s plan a “wrong idea. ... If you want to defend the country, it begins with border security."
A Libertarian, Paul has been one of the most vocal opponents of the National Security Agency's bulk data phone collection program.
'Undercard' debate
At the earlier debate Thursday, former Pennsylvania Senator Rick Santorum criticized Fox and other media outlets for not publicizing the so-called "undercard" debate. He accused the media of taking Iowa voters out of the political process.
Former business executive Carly Fiorina said she was ignoring the media and putting her faith in Iowans to decide what issues are truly important.
Former Arkansas Governor Mike Huckabee complained that hardworking Americans were not getting what he called a "fair shake" in the economy, and he repeated his determination to outlaw abortion.
Former Virginia Governor Jim Gilmore said he was the only military veteran running for president. He said veterans would be treated with respect by the Department of Veterans Affairs when he is president.
But Thursday's spotlight was stolen by the Republicans' leading contender, billionaire real estate mogul Trump. He refused to take part in the debate because of what he alleged was poor treatment by Fox News.
Fox said the flamboyant Trump, a political novice who has surged to the top of political surveys of Republican voters, was welcome at the debate and would be treated fairly. But the network refused to replace moderator Kelly, who angered Trump at an August debate by asking him about slurs he has made over the years about women.
On Thursday, he held firm in his refusal to debate, tweeting, "The 'debate' tonight will be a total disaster — low ratings with advertisers and advertising rates dropping like a rock. I hate to see this."
However, a Fox News spokesperson rejected Trump's statement Thursday, saying: "The debate is completely sold out. No rates have changed and there are no advertisers who have backed out."
Still, Trump was by far the most-searched-for candidate on Google during the first half of the main debate, according to Google Trends data.
At one point, searches on his name outpaced -- by nearly 4-to-1 -- the second-most-searched-for candidate, Rubio.
Trump rally
Trump held a separate event at Drake University for U.S. veterans that coincided with the GOP debate. He said he decided not to appear “out of respect for myself. ... I wanted to be at the debate tonight, but you have to stick up for what’s right."
He told the crowd gathered at his rally: "When you're treated badly, you have to stick up for your rights," adding that "we have to stick up for our country if we're being mistreated."
Trump said his foundation already has raised $5 million for America’s vets. He said he's putting up $1 million of his own money, and that many of his wealthy friends are giving large contributions as well.
Huckabee and Santorum showed up at the Trump event. Each was invited by Trump to speak briefly.
Ken Bredemeier, Ken Schwarz and Mia Bush contributed to this report.
