Former Vice President Joe Biden has a double digit lead over top Democratic competitors Sens. Elizabeth Warren and Bernie Sanders. But CNN's chief national correspondent John King warned in an interview with Boston Public Radio on Tuesday to be wary of the polling.

"In the national polls he is [a front runner.] In the state polls, I think they show a much more competitive race," he said. "I'd just caution everybody to be careful about it. I'm not questioning the hardworking political reporters, it's so early. So you're starting to see some stories about how this is a three-way race, because Biden, Warren and Sanders do have so much of the oxygen right now, but nobody votes for five months."

King said that he's not so sure "the old rules apply" in the era of President Donald Trump, but noted the latest in a line of Biden gaffes: Biden said in a recentinterview with NPR that "details are irrelevant."

"Does it matter? I don't know, but he keeps saying things that break the fact-check machine," said King.

"He's in a lead position in the race," King added. "He's under 40 [percent], so I personally don't call him a front runner."