(CNN) - David Letterman was not amused Wednesday night John McCain hastily canceled his scheduled appearance on the show.
"This doesn't smell right," Letterman said during a routine that only half appeared to be a joke. "This is not the way a tested hero behaves. Somebody's putting something in his Metamucil."
Watch: Letterman skewers McCain
Shortly before he was slated to be on Letterman's show Wednesday, McCain announced he was suspending his presidential campaign to head back Washington to help ensure Congress passes a version of the economic bailout bill.
But Letterman didn't appear to buy the Arizona senator's explanation, and after praising McCain's record as a prisoner of war in Vietnam, said, "This is not the John McCain I know, by God."
"It makes me believe something is going haywire with the campaign," he said. "Something's gotten to him."
Letterman also took a dig at Republican VP candidate Sarah Palin.
"Here's what you do if you are running a campaign in the middle of an economic crisis and it’s about to crater," Letterman continued. "You go back to Washington, you handle what you need to handle. Don't suspend your campaign. You let your campaign go on shouldered by your vice presidential nominee...or is that really a good thing to do? See what I am saying?"
Speaking on NBC's Today Show Thursday morning, McCain spokeswoman Nicole Wallace said, "We deeply regret offending Mr. Letterman, but our candidate's priority at this moment is to focus on this crisis," she said.