Donald Rumsfeld has a new app. But that’s not really what Stephen Colbert wanted to talk to him about Monday night.

At 83, George W. Bush’s former defense secretary has developed a brand new iOS video game called Churchill Solitaire, based on the British prime minister’s unique and strategically advanced version of the classic solo card game. While Rumsfeld may have come to the Late Show to hawk his new product Monday night, Colbert has other plans in mind.

“Let me say, I’m glad I’m not running for president,” Rumsfeld said with a laugh when he sat down with Colbert, before the host pivoted to the new app, taking it less than seriously. “Is he always like this?” Rumsfeld asked the audience, to which Colbert replied, “This is actually much nicer than I usually am.”

“You know this makes you sound like a crack dealer,” the host joked when Rumsfeld described the freemium pay structure in which the game is free at first but costs money as you want to add more features. Proceeds, however, will go to charity.

As Colbert promised, the conversation got significantly more political after a commercial break. “Are you ever upset that there is another Donald out there who is even more famous than you for never apologizing for anything?” he asked.

The former secretary of defense said he has never met Donald Trump and doesn’t quite understand how or why he is “touching a nerve” with so many people. Things got increasingly more tense, however, as Colbert moved on to the decision to go to war with Iraq in 2003, asking if the rise of ISIS was ever even considered by the Bush administration as a “worst-case scenario.”

“I think the disorder in the entire region and the conflict between the Sunnis and the Shia is something that generally people had not anticipated,” Rumsfeld answered. “On the other hand, if you think what Eisenhower said, he said ‘The plan is nothing, planning is everything.’ The point being that anything changes with first contact with a problem.”

Noting that the top two candidates on either side of the aisle all think that going into Iraq was not the right choice to make, Colbert asked, “Do you have any reflection on the decision to go into Iraq? Do you still think it was the right thing to do 12 years later?”

Rumsfeld returned to his old defense of the intelligence on chemical weapons. He did admit that “in retrospect, they didn't find large caches of chemical or biological weapons,” but added that “the UN inspector did say they had the facilities still there, the people were still there who had the capability and the precursors to these weapons were still there.”

Earlier this year, Jeb Bush was tripped up by a question from Fox News’s Megyn Kelly, who asked if “knowing what we know now,” would he have authorized the invasion of Iraq? Colbert told Rumsfeld he thought that was an “unfair” question and decided to rephrase it. “You only know then what you know then,” he said. “You only now know what you know now. And our now is tomorrow’s then.”

Colbert then confronted his guest on his famous quote about “known knowns, known unknowns, and unknown unknowns.” In his mind, there is a fourth option that Rumsfeld leaves out: “unknown knowns, which is the thing that we know, and then we choose not to know or not let other people know we know.”

The host continued to say he would never be so “cynical” to believe that the Bush administration knowingly lied to the American people about weapons of mass destruction in Iraq, but he wanted his guest to admit that there was no “hard proof” in place to justify war.

“There was an unknown known for the American people,” Colbert said. “It was known that there was not hard evidence, but we were presented a partial picture. And that’s the unknown known that we were denied. Do you think that was the right thing to do?”

As Rumsfeld filibustered, Colbert pressed him, asking, “Were there things that the administration, or you, knew that we didn’t learn about out of the best possible intentions, which is there were things that would undermine the case for a war you thought was necessary to save the United States?”

“The president had available to him intelligence from all elements of the government. And the National Security Council members had that information. It was all shared, it was all supplied. And it’s never certain—if it were a fact, it wouldn’t be called intelligence.”

“Wow,” Colbert replied. “I think you answered my question.”

In the end, the sit-down with Rumsfeld was yet another in-depth interview that he could never have pulled off as his old Colbert Report character. It took straightforward, genuine persistence, but the real Stephen Colbert got the job done.