Kelly was actually pretty even-handed during the segment, which featured both Bolton and conservative attorney Andrew McCarthy. She suggested that both the 2003 invasion and the 2011 withdrawal are twin causes for the deteriorating situation in Iraq.
But when Bolton said that past decisions are "irrelevant to the circumstances we face now," Kelly got animated.
"I know, you keep saying that but it actually is relevant to a lot of people out there who are wondering, 'How did we get here?' Is it not relevant to ask, 'How did we get here?'" she asked.
"Well, it's very interesting, but the decision-maker has to look at the environment we have now," Bolton responded, saying it's for that reason he is opposed to President Obama's plan to send 300 military advisers to Iraq.
Kelly wasn't done talking about Bolton's role in the military misadventure.
"You know that a lot of people are out there tonight saying, 'Well, weren't you one of the people who was in favor of going into Iraq in the first place and Is that why you don't want to discuss the past ten years and whether they were worth it?'" she asked.
Bolton said he would be “happy to discuss the past 10 years and we can start 10 years before that if you want,” but he stressed that it's "not the question that America faces today."
The exchange came a day after Kelly's hard-hitting interview with Dick Cheney, during which she told the former vice president that he "got it wrong" on Iraq.
It's a familiar role for Kelly, a former lawyer. While she's certainly done her part to uphold Fox's ideological orthodoxy, Kelly has also distinguished herself from her colleagues by occasionally grilling some conservative guests.
She even went after Fox News contributor Erick Erickson last year after he lamented the rise in breadwinning mothers.
“What makes you dominant and me submissive and who died and made you scientist in chief?” Kelly asked Erickson in a memorable interview.
Kelly told the Washington Post last year that she's "not a political person." Her fellow Fox News host Bill O'Reilly made a similar point earlier this week, telling a gathering at the 92nd Street Y in New York City that Kelly is "not an ideologue."