Donald Rumsfeld has an app. No, it's not called "Angry Kurds," or "Find My WMD" (although wouldn't that be something?). It is a game called "Churchill Solitaire." It is free, and it is not easy.

"No, it's not — it's challenging! It's strategic," the former secretary of Defense said on the phone Sunday, while hustling to Union Station for a train to New York, where on Monday he hawked the app on the "Today" show and talked current events: ISIS ("It's gonna take many, many years to deal with that problem"), if he would be okay with Donald Trump as commander-in-chief ("you bet"), and George H.W. Bush's criticism of his "arrogant" manner ("we were never close").

Rumsfeld's evolution from Eagle Scout to app developer took root longer ago than you'd expect, in 1973, when he was U.S. ambassador to NATO. In Brussels, Rumsfeld met fellow envoy André de Staercke, who had become friendly with Winston Churchill during World War II. The British prime minister taught the Belgian diplomat his rules of solitaire, which involved two decks of cards and a diabolical modification called "the devil's six." De Staercke in turn taught Rumsfeld, who has been playing this complicated version ever since. He likes it for the same reason Churchill did.

Churchill "enjoyed it as a distraction from the many weighty things he was constantly considering," Rumsfeld said. The fact that "it's so much more complex than any card game I know of makes it a particularly interesting diversion."

A couple years ago Rumsfeld's former chief of staff, Keith Urbahn, suggested that the game be loosed from officialdom and shared with the masses as a free app. Revenue from sales of the premium version would go to charities that help members and veterans of the military and their families. Rumsfeld, an avid iPad user, agreed to the project. Churchill's estate gave its blessing.

The game begins with video footage of Churchill in full prime minister mode during the war. Skip that, and then you're dealt a quagmire of cards, left to struggle your way out of them in classic solitaire fashion, with a couple hitches: a point system, a ticking clock, and the aforementioned devil's six — cards separated from the rest of deck that must be moved independently, in order, into the eight piles of aces. Even the "easy" level is challenging.

"You really have to think: 'What is the most important card I oughta have in my mind?'" Rumsfeld said. "And it often is the top card in the devil's six, up above, because if you don't get those off you can't win."

Rumsfeld dictated around 50 memos to help guide Urbahn and a team of developers, he said — a lot of  "look at this, look at that, you fixed the last problem and now there's a new glitch."

A review of the Rumsfeld files finds a scattering of references to the great wartime statesman. In 1963, two months into his first term in Congress, Rumsfeld wrote that a push to award honorary U.S. citizenship to Churchill would set "a bad precedent." On the afternoon of Sept. 10, 2001, he quoted Churchill — ominously, in retrospect: "Nothing surpasses the experience of being shot at. . . and missed." A month after the Sept. 11 attacks, he forwarded George W. Bush some thoughts on Churchill that ended with this: "War is uncertain — a thing where surprises are routine. How wars end is usually just as surprising."

In some ways, the wars that began under Rumsfeld's watch have yet to reach their ends. The devil's six remains uncleared in Iraq and Afghanistan. Once you start playing, though, it's sometimes best to keep the game going.

"On the one hand it's dangerous to do something: It's risky, it's not certain, as Churchill pointed out," Rumsfeld says, referring to U.S. engagement — and disengagement — in regional conflicts. "But on the other hand, not doing something is equally dangerous."

A stumped player of Churchill Solitaire can ask the app for hints, or for redos. If only both were also available in real life.

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