Sen. Mark Kirk (R-Ill.), facing one of the toughest reelection battles in the chamber, added to his list of noteworthy campaign gaffes Thursday night with one of the most awkward moments of his — or perhaps any incumbent senator’s — 2016 campaign.

During their second general-election debate, Kirk's challenger, Rep. Tammy Duckworth (D-Ill.), spoke about her deep connection to military service. “You know, my family has served this nation in uniform going back to the Revolution. I’m a Daughter of the American Revolution,” she said.

“I’ve bled for this nation. But I still want to be there in the Senate when the drums of war sound, because people are quick to sound the drums of war, and I want to be there to say, ‘This is what it costs. This is what you’re asking us to do. And if that’s the case, I’ll go.' Families like mine are the ones that bleed first.”

Kirk was given a chance to respond. “I forgot that your parents came all the way from Thailand to serve George Washington,” he said.

Here’s some context for that comment, courtesy of The Post’s Mike DeBonis:

Duckworth’s mother, Lamai, is Thai, but her late father, Franklin, is a Marine Corps veteran whose family roots trace to before the American Revolution. Rep. Duckworth was severely wounded in the Iraq War, losing her legs while serving as a helicopter pilot. She did not respond to Kirk before the moderator moved on to the next question.

The awkwardness of that four seconds or so of silence actually cannot be related via transcript; you can see it for yourself below:

Democrats pounced, with a Democratic Senatorial Campaign Committee spokeswoman calling the remark “offensive, wrong and racist,” and demanding an apology.

There was no apology in the statement issued by Kirk campaign spokeswoman Eleni Demertzis, reported DeBonis.

“Senator Kirk has consistently called Rep. Duckworth a war hero and honors her family’s service to this country,” Demertzis said. “But that’s not what this debate was about. Rep. Duckworth lied about her legal troubles, was unable to defend her failures at the VA and then falsely attacked Senator Kirk over his record on supporting gay rights.”

Kirk has delivered an eyebrow-raising string of comments over the past few years, including a reference to Sen. Lindsey Graham (R-S.C.) as a “bro with no ho.” Last year, during the funding fight over the Department of Homeland Security, he said Republicans should build coffins outside Democratic offices if there were a terrorist attack and tell them they were “responsible for these dead Americans.” And he spoke of wanting to support African American entrepreneurs so people did not feel a desire to “drive faster” through “the black community.”

Kirk has also drawn attention this year for his decision to endorse — then, ahead of the GOP convention, unendorse — Republican presidential nominee Donald Trump. He drew fire this week for refusing to say whether he still planned to write Gen. David Petraeus’s name in as his presidential pick this year instead of Trump’s.

“I said that largely out of total frustration,” he told Chicago radio station WBEZ of that plan. “The joke I’ve seen going around is, ‘If you had a rowboat and it sprung a leak with Hillary and Trump in it and it sank, who would win?’” He said he didn't have a candidate at the moment, and was ”pretty frustrated by the choice that we have now.”