From NBC News:

Former Secretary of State John Kerry — one of Joe Biden's highest-profile endorsers — was overheard Sunday on the phone at a Des Moines hotel explaining what he would have to do to enter the presidential race amid "the possibility of Bernie Sanders taking down the Democratic Party — down whole."

Sitting in the lobby restaurant of the Renaissance Savery hotel, Kerry was overheard by an NBC News analyst saying "maybe I'm f---ing deluding myself here" and explaining that in order to run, he'd have to step down from the board of Bank of America and give up his ability to make paid speeches. Kerry said donors like venture capitalist Doug Hickey would have to "raise a couple of million," adding that such donors "now have the reality of Bernie."

Asked about the call later on Sunday, Kerry said that he was "absolutely not" contemplating joining the Democratic primary race. He reiterated this sentiment in a tweet later, saying that "any report otherwise is f---ing (or categorically) false."

As I told the reporter, I am absolutely not running for President. Any report otherwise is fucking (or categorically) false. I’ve been proud to campaign with my good

friend Joe Biden, who is going to win the nomination, beat Trump, and make an outstanding president. — John Kerry (@JohnKerry) February 2, 2020

"Everyone knows that John Kerry is all in for us," Symone Sanders, a senior adviser to the Biden campaign, told NBC News.

It’s not clear how serious Kerry was on the call about jumping into the race. But that he would even discuss the possibility suggests that prominent members of the Democratic Party remain deeply unsettled by the current field, Sanders' strength in the polls, and the ability of any candidate to defeat President Donald Trump.

It also suggests that Kerry, who has campaigned with Biden in Iowa and New Hampshire, may be nervous about the former vice president's chances ahead of Monday's first-in-the-nation primary caucuses. At a North Liberty, Iowa, campaign event on Saturday, Kerry spoke both after and for longer than Biden did.

Kerry was the Democratic presidential nominee in 2004, losing to President George W. Bush. He got 251 electoral votes, compared to Bush's 286.

Kerry has served as one of the former vice president's top surrogates in the 2020 race. Biden holds a less than 4-point lead over Sanders in the RealClearPolitics average of national Democratic primary polls but trails the Vermont senator in the Iowa and New Hampshire polling averages.