Transcript for ABC News' Jonathan Karl: Free press is a big part of what makes America great

We'll be right back. Cc1 Test message I would like to close with a little perspective. There is nothing new about a president of the United States criticizing or even vilifying the press. Even Thomas Jefferson, the same Thomas Jefferson who wrote the declaration of Independence and whoa our liberty depends on freedom of the press. Even Thomas Jefferson, when he was a few years into his own presidency was so upset about what was being written about his administration said nothing can now be believed seen in a newspaper. Teddy Roosevelt once wrote, to announce there must be no criticism of the president or that we are to stand with the president right or wrong is not only unpatriotic and servile, buzz is morally treasonable to the American public. I couldn't agree more. He wrote that nearly a decade after he wrote office. When he was still in the white house, he coined the term muck Rakers to denounce inves gate I have journalists that he felt they were missing the good in the world. Including the good he was doing as president. Such negativity in the press, Roosevelt said, is one of the most potent forms of evil. That brings me to president Donald Trump. Who has take. Presidential criticism of the news media to yet another level. In a way it surprised me. The Donald Trump I knew as a young reporter in New York was nothing if not media friendly. For most of the past Republican primary, he was the most accessible candidate. No one else was close. We saw 17 reporters called on on Thursday. Many that he knew would ask tough questions. But now, the president has declared the press the enemy of the American people. I've reported in countries where leaders not only complain about a critical press but also try to shut it down. Throwing reporters in prison or worse. I've seen my colleagues risk they're lives and with increasing frequency, lose their lives in their pursuit of the truth. We're not about to stop doing our jobs because yet another president is unhappy with what he reads or hears or sees on TV news. There is a reason the founders put freedom of the press in the very first amendment to the constitution. As long as American democracy remains healthy, there will be reporters willing to pursue the truth, even if that means incurring the wrath of the most powerful person in the world. A free press is not the enemy of America. It's a big part of why makes America great. That's all for us today. Thank you for sharing part of your Sunday with us. Check out "World news tonight." And have a good day.

This transcript has been automatically generated and may not be 100% accurate.