I remember that story. Funny thing is Chang = Chiang Kai-shek, and it's an outgrowth of Bush Sr. using the phrase "unleash Chiang" in tennis games.
From a
memoir about George HW Bush written by his daughter Doro:
By the way, he still uses a phrase in his tennis games that he picked up in China: "unleash Chiang"--a reference to Chiang Kai Shek, the nationalist leader exiled on Taiwan--as slang for Let's start this game and serve the big one. He had a bit of a weak serve, and it was his way of making fun of it: Time to unleash Chiang!
"Picked up in China" means during Bush's time as the ambassador to the PRC in the 70's, so it's almost certainly a joke on US hardliners who thought Chiang could retake mainland China if only America would support him. So a sarcastic reference to the ROC gradually morphed into an inspirational mystic Asian warrior.