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Sen. John McCain seemed to hit President Donald Trump during an interview about the Vietnam War on Sunday, criticizing Americans from "the highest income level" who were able to obtain draft deferments for ailments like a “bone spur.”

Trump received a draft deferment in 1968 for bone spurs in his heels.

"One aspect of the 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 during an interview with C-SPAN that aired Sunday.

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"That is wrong. That is wrong. If we’re going to ask every American to serve, every American should serve," the six-term Arizona Republican added.

McCain, who is fighting brain cancer, did not mention Trump by name during the interview.

Trump, however, was reported to have received five draft deferments during the Vietnam War: Four for education and one for having had bone spurs in his feet.

McCain, on the other hand, spent several years as a prisoner-of-war in North Vietnam after his plane was shot down in 1967.

McCain revisited the topic during an interview Monday morning with ABC's "The View," saying he didn't see Trump "so much a draft dodger, as I feel that the system is so wrong that certain Americans can evade their responsibility to serve the country."

"What I was trying to say is one of the great inequities of the Vietnam conflict is the lowest income Americans went and fought and were drafted, and those who were wealthy enough to get a doctor to say, 'Hey, you've got a bone spur or migraines,' or whatever it is...then they were excused," he said.

McCain's round of comments marked the latest exchange in a long-running feud between the two men that kicked off in July 2015, when Trump said McCain was "not a war hero."

"He was a war hero because he was captured. I like people who weren’t captured," Trump said.