Text of the letter Hoover is writing: "Could you all please stop hating on me? I tried. You wouldn't have done any better. kthxbai."
Though I'd intuitively agree with the proposition that, say, Canadian leaders know more about American political history than American leaders know about past Canadian election, I think Matt Yglesias may be slightly overstating the significance Bob Rae comparing Stephen Harper to Herbert Hoover. "I’m not sure I’ve ever heard a U.S. politician draw an analogy to any foreign leader other than Churchill or Hitler," says Matt. But I'd add one foreign politician we hear of often: Neville Chamberlain. And Hoover is, popularly, the Neville Chamberlain of the Great Depression (though I'd argue that Hoover gets an undeservedly terrible rep). Invoking Hoover may not suggest deep engagement with American history. Rather, there are a few 20th Century catastrophes that most folks know about, and he's the villainous politician behind one of them. 
