On the 'Late Show' (video below), David Letterman told guest Bill O'Reilly that America turned Iraq into a hotbed of terrorism, which didn't exist before the U.S invasion.
Surprisingly, O'Reilly essentially agreed with him that the U.S. invasion was a mistake. O'Reilly said that he supported it initially based on claims there were weapons of mass destruction in Iraq, which turned out to be a false claim by the Bush Administration.
Letterman tried to celebrate their moment of agreement with a high-five, but O'Reilly refused: "We're having a good conversation. Sit down."
Letterman persisted and O'Reilly finally gave him the high-five, prompting Dave to say: "No wonder Cheney won't come on your show, Mr. Grouch!"