US Senator McCain, defending the media against the latest attack by President Donald Trump, has warned that suppressing the free press was "how dictators get started".
The Arizona Republican, who was the Republican presidential nominee for the 2008 election and is afrequent critic of Mr Trump, was responding to a tweet in which Mr Trump accused the media of being "the enemy of the American people".
Modern democracy was built, in part, on a free press, Mr McCain said in an excerpt of an interview with NBC's Meet the Press.
"The fact is we need you. We need a free press. We must have it. It's vital."
"If you want to preserve - I'm very serious now - if you want to preserve democracy as we know it, you have to have a free and many times adversarial press. And without it, I am afraid that we would lose so much of our individual liberties over time. That's how dictators get started," he said.
"They get started by suppressing free press. In other words, a consolidation of power. When you look at history, the first thing that dictators do is shut down the press. And I'm not saying that President Trump is trying to be a dictator. I'm just saying we need to learn the lessons of history," Mr McCain said.
US Senator Jeanne Shaheen, a Democrat from New Hampshire, told a conference on Sunday she was concerned about Trump's comments.
"The real danger is the president's criticism of the media," Ms Shaheen said. "A free press ... is very important to maintaining democracy, and efforts on the part of a president to undermine and manipulate the press are very dangerous."
US lawmakers' comments came days after the president held a raucous news conference at which he repeatedly criticised news reports about disorder in the White House and leaks of his telephone conversations with the leaders of Mexico and Australia.
German Chancellor Angela Merkel emphasised the importance of a free press at the conference on Saturday, saying, "I have high respect for journalists. We've always had good results, at least in Germany, by relying on mutual respect."