“Late Show” host Stephen Colbert on Thursday said he thinks he knows the exact moment that cost Homeland Security Secretary Kristi Noem her job.

Noem was fired earlier in the day by President Donald Trump after she testified this week in contentious House and Senate committee hearings in which she was grilled by Democrats and Republicans alike.

But one exchange stood out: When Sen. John Kennedy (R-La.) asked about a $220 million ad campaign that featured Noem wearing chaps and a cowboy hat on horseback.

“She passed the blame on to definitely the wrong guy,” Colbert said, and rolled a clip of Noem insisting that Trump himself approved of those ads.

“No,” Colbert warned. “Don’t ever blame anything on Donald Trump.”

Then he broke out his impression of the president.

“Ladies and gentlemen, it has come to my attention that Kristi Noem is just days away from developing a nuclear weapon,” he said. “We have no choice but to strike and strike hard.”

With Noem on the outs, Colbert said it was time to focus on the future.

“You know which Cabinet member I hope Trump fires next?” he asked. “All of them!”

The audience cheered.

“Clean slate,” he said. “Sweep it.”

Narrowing it down to a single person, however, Colbert did have an idea on who should go next.

Check it out in his Thursday night “Late Show” monologue:

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