Sen. John McCain tweeted out a New York Times story Sunday morning, in which he was labeled the "unfettered voice against Trumpism."

"I'm doing what I think is right for the country," McCain is quoted as saying in the Times story. "I don't work for Donald Trump, and I don't work for his administration."

Why it matters: McCain and Trump have butted heads since the 2016 campaign, during which Trump said he likes "people who weren't captured," referring to McCain’s five years spent as a POW. McCain, in recent months, has been biting back both through his rhetoric and by helping to thwart the president's agenda.

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