Donald Rumsfeld, the former secretary of defense, has an app — a card game called Churchill Solitaire — that’s free but not easy. While serving in Brussels as U.S. ambassador to NATO in 1973, he learned the game from fellow envoy André de Staercke, who was taught by his friend Winston Churchill. The game, played with two decks, begins with video footage of Churchill in full prime minister mode during World War II. 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 diabolical 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. A stumped player can ask the app for hints, or for redos.