Senator John McCain's relationship to President Donald Trump is hard to describe. Trump has insulted McCain and questioned his heroism in the past, and the senator has helped kill some of the president's major proposals, such as repealing Obamacare. However, McCain has also supported almost all of the president's other policies and has not directly confronted Trump on many issues. And it looks like McCain's passive-aggressive tactics are continuing.

McCain recently appeared on a CSPAN show about the Vietnam War. During his appearance, he discussed people who received dubious doctor evaluations to avoided getting drafted, and just happened to mention the very "medical issue" that Trump used to avoid joining the Army.

"One aspect of the [Vietnam] conflict by the way that I will never ever countenance is that we drafted the lowest income level of America and the highest income level found a doctor that would say that they had a bone spur," McCain said. "That is wrong. That is wrong. If we are going to ask every American to serve, every American should serve."

During Vietnam, Trump received five deferments from serving in the armed forces. He avoided the first four because he was still in college, and the fifth one was due to "bone spurs in his heels."

McCain and Trump have butted heads on Vietnam military service in the past. While on the campaign trail, Trump criticized the senator and questioned his heroism by saying, "I like people who weren’t captured," a reference to McCain's capture by the VietCong for more than five years during the conflict.

Of course, it's not clear if McCain was making a dig at the president or if that was just the first silly medical issue he could think of. But I'm guessing Trump will take great offense to it and respond on Twitter with something insulting about the war hero.

And then McCain will vote for Trump's tax plan, and we'll all remember that this is just a giant charade to hide the fact that the Republicans are perfectly fine with Trump being president.

(h/t Buzzfeed)