"I'm not endorsing Joe because I've known him a long time. I'm endorsing him because I know him so well," Kerry, the 2004 Democratic presidential nominee, said in a telephone interview ahead of the formal announcement of his endorsement.
Kerry will join Biden on the campaign trail on Friday in Iowa, where the former vice president is in the midst of a week-long bus tour of the state, and in New Hampshire on Sunday, according to the Biden campaign. The former secretary of state said he would continue to campaign for Biden in the weeks and months ahead.
"The world is broken," said Kerry, who was made available for the interview by Biden's campaign. "Our politics are broken. The country faces extraordinary challenges. And I believe very deeply that Joe Biden's character, his ability to persevere, his decency and the experiences that he brings to the table are critical to the moment. The world has to be put back together, the world that Donald Trump has smashed apart."
Kerry cited Trump's trip to the NATO summit in the United Kingdom this week. "The petulance and smallness and ridicule that he invited is very dangerous for all of us," Kerry said. "And that just underscores the urgency of people recognizing the assets that Joe Biden brings to the table."
He also said he felt strongly that Biden could beat Trump next November. "The president knows it," he added. "And that's why he was so busy dispatching Rudy Giuliani and engaging in unconstitutional behavior."
The endorsement by the former secretary of state dovetailed with another effort by Biden to highlight disdain for Trump on the world stage, including at the just-concluded NATO meetings, where some foreign leaders were filmed mocking him.
In a lancing ad posted on Twitter on Wednesday night, Biden used that video and other Trump foreign policy conflicts, juxtaposed against pictures of Biden dealing soberly with world leaders and stepping off Air Force Two as vice president.
In his narration, Biden called Trump "insincere, ill-informed, corrupt, dangerously incompetent and incapable, in my view, of world leadership." By early Thursday, the video had been viewed more than 5 million times.
Kerry's endorsement comes at a moment when Biden has drawn criticism for a lack of consistency as a candidate. He is struggling in both Iowa and New Hampshire, where he began the campaign leading the field and has slipped significantly, according to the RealClearPolitics poll average. The Iowa bus tour is part of the Biden campaign's effort to turn around his candidacy.
The announcement marks the second notable endorsement for Biden by a member of former President Barack Obama's Cabinet. Tom Vilsack, the former agriculture secretary and former Iowa governor, and his wife, Christie, endorsed Biden late last month and have campaigned with him in Iowa.
Sixteen years ago, in late 2003, then-Sen. Kerry was in a similar situation to that of Biden today, with his presidential campaign lagging in Iowa - and struggling nationally far more than Biden's. Kerry revived his candidacy early in 2004, winning Iowa and then New Hampshire and from there cruising to the nomination. Asked what Biden should do to get his campaign moving, Kerry said, "He needs to do exactly what he's doing now."
He also defended Biden against criticism, saying the media has sometimes created characterizations that overstate the candidate's problems. He pointed to Biden's resiliency in national polling and to the breadth of Biden's coalition and in particular his support from African Americans.
Kerry conceded that Biden has sometimes appeared to struggle to find words in the candidates' debates but dismissed it as insignificant. "Who hasn't done that,over a lifetime?" he said. "He is just honest, straightforward. He's a Joe that represents the middle class of America and understands them, I think, in ways that will reach way beyond Donald Trump in a general election."
Kerry said his decision to back Biden is not meant as criticism of any of the other Democrats in the race, including two from his home state of Massachusetts - Sen. Elizabeth Warren and former Gov. Deval Patrick. "I like Elizabeth enormously. I worked very hard to help her win her seat. And I like Deval. I worked closely with him as governor. I just think Joe is the person for the moment," he said.
Kerry was secretary of state in 2014 when Biden's son Hunter joined the board of the Ukrainian energy company Burisma. At the time, Biden was the point person leading an effort, backed by U.S. allies, to fire the Ukrainian prosecutor, who was regarded as an obstacle to attacking corruption in the country. While there has been no proof of wrongdoing by the Bidens, Trump and his loyalists have seized on their actions; the president's demand that Ukraine's new leader investigate the Bidens has formed the nucleus of the ongoing House impeachment inquiry.
Republicans have raised the prospect of calling both Bidens to appear at Senate hearings, but Kerry said he wasn't worried about that possibility. "I'm not concerned about that, and I think there won't be very much," he said. "You guys will discern pretty quickly how craven and empty it is. Obviously, this could be a tough fight. But I think Joe is up to being tough."
When Kerry was struggling in late 2003, he watched as Howard Dean, the former governor of Vermont and the presidential front-runner, picked up high-profile endorsements, including from former Vice President Al Gore and then-Sen. Tom Harkin of Iowa. Those endorsements proved of little value in the end for Dean.
"I think the value of it [the endorsement] is that it stops people, hopefully, and provides some food for thought. I have never presumed anybody can tell anybody else how to vote," he said. "I don't approach it that way. It's a recommendation and a rationale. . . . People will make their own judgments."