GEOFF BENNETT: Last night's debate brought four GOP presidential hopefuls to the University of Alabama's campus for their last face-off of the year.

And, once again, the leading Republican contender, Donald Trump, skipped it.

Laura Barron-Lopez has this recap.

LAURA BARRON-LOPEZ: In Alabama, the four candidates on the debate stage largely ignored the GOP presidential front-runner that they're trailing by more than 40 points.

It wasn't for lack of trying by former New Jersey Governor Chris Christie.

FMR.

GOV.

CHRIS CHRISTIE (R-NJ), Presidential Candidate: We're 17 minutes into this debate, and except for your little speech in the beginning, we have had these three acting as if the race is between the four of us.

LAURA BARRON-LOPEZ: He issued a dire warning about the stakes of electing former President Donald Trump a second time.

FMR.

GOV.

CHRIS CHRISTIE: I'm in this race because the truth needs to be spoken.

He is unfit.

This is a guy who just said this past week that he wants to use the Department of Justice to go after his enemies when he gets in there.

And there is no bigger issue in this race, Megyn, than Donald Trump.

LAURA BARRON-LOPEZ: Instead, entrepreneur Vivek Ramaswamy repeated Trump's lies about 2020 and embraced a racist conspiracy theory that claims white Americans, at the direction of elites, Democrats, or sometimes Jewish people, are being replaced by people of color.

VIVEK RAMASWAMY (R), Presidential Candidate: That the Great Replacement Theory is not some grand right-wing conspiracy theory, but a basic statement of the Democratic Party's platform, that the 2020 election was indeed stolen by big tech.

LAURA BARRON-LOPEZ: It's a conspiracy theory that was cited by the white men who carried out mass shootings in Pittsburgh, El Paso, and Buffalo.

And former South Carolina Governor Nikki Haley, who is gaining traction in the polls and with GOP donors, confronted Trump on China, but little else.

NIKKI HALEY (R), Presidential Candidate: This is where Trump went wrong.

Trump was good on trade.

But that's all he was with China, because here he allowed fentanyl to continue to come over.

He continued to allow them to take -- he would give them technology that would build up their military and hurt us.

He allowed the Chinese infiltration for them to buy up farmland, to put money in our universities, and to continue to do things that were harmful for America.

LAURA BARRON-LOPEZ: Tied with Haley for second place, Florida Governor Ron DeSantis defended his past pledge to shoot undocumented people crossing the border if they have backpacks.

GOV.

RON DESANTIS (R-FL), Presidential Candidate: The commander in chief not only has a right, you have a responsibility to fight back against these people.

QUESTION: And does that mean shooting first?

GOV.

RON DESANTIS: It means you're going to categorize them as foreign terrorist organizations.

LAURA BARRON-LOPEZ: And spent much of his time positioning himself to the right of Haley.

GOV.

RON DESANTIS: Nikki Haley said the other day there should be no limits on legal immigration and that corporate CEOs should set the policy on that.

NIKKI HALEY: That's not true.

Quit lying.

GOV.

RON DESANTIS: There needs to be limits on immigration.

LAURA BARRON-LOPEZ: In fact, it was Haley, not Trump, who came under repeated fire.

VIVEK RAMASWAMY: Nikki is corrupt.

GOV.

RON DESANTIS: And you have other candidates up here like Nikki Haley.

She caves any time the left comes after.

NIKKI HALEY: And I love all the attention, fellows.

Thank you for that.

LAURA BARRON-LOPEZ: With the Iowa caucuses just 39 days away and only two more primary debates on the calendar, candidates will blanket early states, in the hopes of toppling the current front-runner.

For the "PBS NewsHour," I'm Laura Barron-Lopez.