The fight isn’t really between two men. It’s between two takes on what matters most in this messy world. I might as well be blunt: It’s between the high road and the gutter. McCain has always believed, to his core, in sacrifice, honor and allegiance to something larger than oneself. Trump believes in Trump, and whatever wreckage he causes in deference to that god is of no concern.

“Trump is in every single way the opposite of John McCain,” Bob Kerrey told me recently. “He may be the opposite of every president we ever had.” Kerrey and McCain both served in Vietnam, they overlapped in the Senate and they stay in touch. So Kerrey knows that Trump has caused McCain no small measure of anguish, but less because of Trump’s crassness and the daily tragicomedy of his administration — this, too, shall pass — than because of “the impact on democracy.” It could be enduring, and it could be profound.

That’s why a patriot like him could never sit this one out.

Trump finds McCain’s biography and example threatening; that was obvious in an insult in the summer of 2015, just a month into Trump’s presidential campaign. At a forum in Iowa, Trump mocked McCain’s many years as a prisoner of war in Vietnam — years during which McCain refused offers of release because he didn’t want to be a tool of North Vietnamese propaganda — by saying: “He’s not a war hero. He’s a war hero because he was captured. I like people that weren’t captured.”

McCain brushed it off. “He never mentioned it,” Gen. David Petraeus, who sits on the board of the McCain Institute for International Leadership at Arizona State University, told me. “I raised it with him one time. I said, ‘I just want to assure you that everyone I know — and I — regard you as an extraordinary hero.’ He said: ‘I know. It’s nothing.’”

It’s all too easy, in the context of Trump, to idealize political leaders who came before him and airbrush their flaws. McCain has his share, including the occasional rashness reflected in his selection of Sarah Palin as a running mate in 2008. Did she help pave the way for Trump? What a cruel irony if so.