I will never forget the moment when I realized that President Trump had transformed the way we think about political scandals.It was in September 2019, right after Trump released the memorandum of his July 25, 2019, call with Volodymyr Zelensky, the president of Ukraine. There, in black and white, was one of the clearest examples of an improper quid pro quo in foreign affairs that I’d ever seen.Zelensky told Trump that he would like to purchase Javelin anti-tank missiles for Ukraine. Trump responded with his own request. “I would like you to do us a favor,” he said, and proceeded...