Here are five key moments from the undercard debate:
1. Fiorina Saves Her Best One-liners for Clinton
“Listen, if my husband did what Bill Clinton did, I would have left him long ago,” Fiorina said, adding that Clinton ”has escaped prosecution more times than El Chapo," referring to the notorious Mexican drug lord Joaquin Guzman.
And in answering a question on the threat of ISIS, Fiorina used the former secretary of state’s words against her.
“You are saying to every adversary and every terrorist organization on the planet, it's open season. That, Mrs. Clinton, is what difference it makes,” Fiorina said, paraphrasing a remark Clinton made at her 2013 Benghazi hearing.
2. Rick Santorum Rejects ‘Undercard’ Label
Former Pennsylvania Sen. Rick Santorum argued at the debate that “undercard” was akin to four-letter word.
“You know, listening to what your network was talking about prior to this race, this debate, reminded me of the coverage that many on this floor are getting,” he said, chastising the moderator. “This debate was called the undercard debate -- the undercard debate. It wasn't advertised significantly. In fact, the entire hour lead-up to this, there was no conversation about any of the four people on this debate stage."
Later, he implored Iowans to ignore the polls and “pick the leader you know is best for this country.”
3. Mike Huckabee and a Guy Named Thomas
Instead, he emphasized he isn’t “bank-rolled by the corporatists” like Goldman Sachs and AIG.
“I'm sponsored by people like Thomas, a part-time Uber driver in Pennsylvania who sent me $25 this week,” he said. “He is between jobs. He is driving an Uber car. But he believed in what I'm talking about enough that even on a limited, part-time income, he sent me $25 to help in my campaign. I'll stand with the Thomas of the world any day.”
4. Jim Gilmore: ‘Did You Miss Me?’
“Did you miss me? Did you skip me?" Jim Gilmore interjected as the Fox moderator directed a question to fellow GOP contender, Mike Huckabee.
While the former Virginia governor may not have shined on the presidential debate stage, his finest hour was on social media.
Gilmore became a trending topic on Twitter minutes into the debate. Why? Twitter users were interested to know who the presidential candidate was.
5. Candidates Cornered About the Caucuses
Santorum, who belatedly won the Iowa caucuses in 2012, was asked if Feb. 1, 2016, was his last stand, he chastised the moderators for asking, adding: “What Iowans deserve,” Santorum said, “is to hear from every candidate on an equal footing.”
Huckabee was asked why he wasn’t doing better in the polls: “I don't think it's that the message isn't working. I think the message isn't getting out,” he said.
And Gilmore acknowledged he wasn’t focused on Iowa: “I am beginning my campaign in New Hampshire, and I decided to do that based upon the process that is in place in Iowa.”