They strolled through the construction site like the old friends they are, Mayor Martin J. Walsh and the former vice president, Joe Biden, interchangeably wrapping a hand around the other’s shoulder, greeting worker after worker on Wednesday afternoon.
Then, in an unannounced move, the two of them strayed from their tour of the nearly completed Martin’s Park on Sleeper Street and marched the half-mile to the Massachusetts Fallen Heroes Memorial, surrounded by a crowd of media cameras and other followers — their own little parade on a sunny afternoon in the Seaport.
In the jubilance of the moment, Walsh could have announced that he and his team are behind Biden, who polls show as the early front-runner in a crowded field for the Democratic nomination for president. But he didn’t. At least not yet.
Not with so many other candidates, including Elizabeth Warren, the senior senator from Massachusetts, very much in the mix.
“I’m still going to wait and see; I’m going to give it a little more time to see what happens,” the mayor told reporters afterward, once Biden had jumped in his car to head to another event and, eventually, two evening fund-raisers.
The hesitance shows the fine line Walsh, a mayor who boasts a longtime, close relationship with the former vice president, has to walk in a heated Democratic primary race. Several of the candidates can claim Walsh as a friend, and they would be glad to have his endorsement, which would presumably come with the former union leader’s connections to local labor and the city’s top political donors.
Warren, the first major candidate to announce a campaign for president, has been close to Walsh since he first backed her for Senate in 2012, when the mayor was a state representative on Beacon Hill.
The mayor was an early fan of Kamala Harris, the junior senator from California, who is also running; she met with him recently in Boston, the mayor said.
Another member of Congress from Massachusetts, Representative Seth Moulton, is also seeking the Democratic nod.
Walsh said that he is also friendly with Pete Buttigieg, the mayor of South Bend, Ind., who has blown past expectations in his campaign for the presidency. Buttigieg visited Boston last year for the annual meeting of the US Conference of Mayors and attended the city’s popular LGBT Pride parade and festival with Walsh.
But none of these relationships have the history that Walsh has with Biden, whom he first met in 1997. They grew closer during Biden’s vice presidency, as he sought to establish connections with the country’s mayors on policy issues such as climate change and community policing.
Walsh said that he would regularly see Biden in Washington. “The relationship took off from there,” Walsh said Wednesday.
The two have had frequent public appearances over the years. In 2018, Biden came to Boston to preside over Walsh’s inauguration for a second term. The vice president flattered him with praise, calling Walsh “a mayor who will never forget where he came from.”
In 2017, while in the area for a speech at Harvard, Biden dined with Walsh at the No Name restaurant in the Seaport. Biden even called into the St. Patrick’s Day Breakfast in 2015.
In 2014, on the first anniversary of the Boston Marathon bombings, Biden met with local families, including the family of Martin Richard, the 8-year-old boy who was killed in one of the blasts. On Wednesday, he met with the Richard family again, during a tour of the waterfront park that was built in Martin’s honor.
Walsh held up the park as the type of work cities could do to help cope with climate change, with resiliency designs, and Biden said the work goes to the vision that he outlined in a $1.7 trillion plan to address climate change.
“The thing that people don’t get, that the mayor has figured out ahead of everyone else, is that this creates good jobs,” Biden told reporters, taking the opportunity to praise his old friend.
Days after Biden announced his candidacy, in April, Walsh acknowledged the conflict of having friends run in the same high-profile campaign. He said that Biden had already told him he would run, and that he understood the sensitivity of local politics in Massachusetts.
“It’s kind of strange to be in a position where you have a relationship with a few of the candidates who are running, personally,” the mayor said in an interview at the time.
He said, “The one thing I’m happy about, is there’s a lot of great conversations in the race, and they’re elevating the conversation . . . Vice President Biden brings a different perspective to the race than some other people might have, so we’ll see what happens.”
Paul Maslin, a Democratic pollster, said that if Walsh endorses a front-runner like Biden, it can’t hurt him — especially because they are close friends.
Sure, Warren is the hometown senator, Maslin said, but she can’t yet claim the type of political authority over the state that Edward M. Kennedy, the late senator, claimed.
“Every bit of politics is ultimately guided by relationships,” Maslin said. “If you feel good about someone, you trust them, you have a connection . . . why not?”
But Erin O’Brien, a political science professor at the University of Massachusetts who supported Walsh’s election in 2013, said the mayor should stay out. She said she hasn’t spoken with him about the race, but noted that he has not had much recent success with endorsements. (Walsh backed then-congressman Michael Capuano, who was ousted by former Boston city councilor Ayanna Pressley in a primary last year. Walsh also supported Warren Tolman over Maura Healey for attorney general in 2014; Healey won.)
Even if Walsh and Biden are best friends, she said, the mayor would once again be seen as supporting a white, established man over an up-and-coming woman. “The smart move is to stay out of the nomination game and mobilize his campaign apparatus for whomever the Democratic nominee is,” she said.