"The phrase "fake news" - granted legitimacy by an American president - is being used by autocrats to silence reporters, undermine political opponents, stave off media scrutiny and mislead citizens", the senator wrote in The Post.
McCain cited a recent Committee to Protect Journalists report, noting that 2017 saw a rise in attacks on journalists worldwide.
McCain's op-ed lands ahead of Trump's so-called "Fake News Awards", an event he invented and has been promoting on Twitter. "But constant cries of "fake news" undercut this type of reporting and strip activists of one of their most powerful tools of dissent".
Trump tweeted on January 2 the announcements were due on January 8 before he postponed them until Wednesday January 17. When asked about the ceremony on Tuesday afternoon, White House press secretary Sarah Huckabee Sanders said the awards were a "potential event".
Trump has still not begun the award show as of 7:30 p.m. Wednesday.
"Covered in real fake gold and made in "Gina" the mock Trump announced while holding the award.
Chrissy Teigen hosted her own Fake News Awards when President Trump failed to do so.
Flake also compared Trump's attacks on the news media to the rhetoric of late Soviet dictator Joseph Stalin and highlighted the longstanding consequences for Trump's attacking the truth. For they are shameful, repulsive statements.
He criticized the President for calling the news media the "enemy of the people", calling it "an assault as unprecedented as it is unwarranted".
"Ultimately", McCain concluded, "freedom of information is critical for a democracy to succeed".
"So that's the press doing its job and it's highly inconvenient for him".
"More than two-fifths of evening news coverage of the President (43%) focused on controversies, not policies, with the Russian Federation investigation alone accounting for one-fifth of all Trump coverage (1,234 minutes)", read one of the study's findings.