"What the Russians exploited, but it was already here, is we are operating in completely different information universes," Obama told Letterman in the first episode of Letterman's new Netflix series "My Next Guest Needs No Introduction." "If you watch Fox News you are living on a different planet than you are if you listen to NPR."
The comment came after Letterman asked, "Let's just say there's a democracy and the voting process is being monkeyed with by foreign countries. ... Hypothetically, what is more damaging to that democracy: Would it be the diminishment by the head of democracy of press, or would it be somebody screwing around with the actual voting process?"
"One of the biggest challenges to our democracy is the degree to which we don't share a common baseline of facts," Obama said.
He went on to discuss the use of social media in his 2007 campaign, noting that at the time people didn't realize the power -- and potential dangers -- of platforms like Twitter and Facebook.
"We were some of the earliest adapters of social media," he said of his campaign staff. "And we were reliant on a bunch of 22- and 23-year-olds, and volunteers ... they were communicating entirely through social media. We essentially built what ended up being the most effective political campaign probably in modern political history. So I had a very optimistic feeling about it. I think what we missed was the degree to which people who are in power ... can in fact manipulate that and propagandize."
Letterman then quipped: "I was under the impression that Twitter would be the mechanism by which truth was told around the world."
Social media has also led to political polarization, Obama said.
"If you are getting all your information off algorithms being sent through phone and it's just reinforcing whatever biases you have, which is the pattern that develops," he said, "at a certain point, you just live in a bubble, and that's part of why our politics is so polarized right now. I think it's a solvable problem but I think it's one we have to spend a lot of time thinking about."
The interview, which was about an hour long, debuts on Netflix on Friday. Guests scheduled for the rest of Letterman's shows include George Clooney, Malala Yousafzai, Jay-Z, Tina Fey and Howard Stern.