WASHINGTON — Representative Joseph P. Kennedy III is weighing a primary challenge to Senator Edward J. Markey, according to a person close to Kennedy and a Democratic congressional source, a move that would upend Massachusetts politics and trigger a potentially divisive intraparty fight.
Kennedy will make a decision about whether to run in the coming weeks, the person close to him said, adding that the four-term congressman began weighing the idea recently after he was approached by people urging him to make the bid.
The 38-year-old scion of the nation’s most famous political family paid for a poll in recent weeks testing a matchup against the 73-year-old Markey, according to two Democratic operatives familiar with the poll. The survey found voters favored Kennedy by a small margin, according to several people familiar with the results.
Publicly, Kennedy’s team has said he plans to run for another term for the Fourth Congressional District, which stretches from Brookline and Newton south to Fall River. His behind-the-scenes consideration of a high-profile primary challenge, however, is another sign of how the state’s longstanding tradition of respecting incumbents is ending, a demise hastened by the 2018 midterm elections, which showed voters clamoring for fresh faces.
Kennedy would hardly be in the mold of insurgent candidates Ayanna Pressley and Alexandria Ocasio-Cortez, who knocked off veteran House Democrats in primary upsets in part by calling for new and younger voices in the party. He is the grandson of former US attorney general and senator Robert F. Kennedy, who was assassinated in 1968 while campaigning for president. If he runs, Kennedy would be following a familiar family path toward higher office.
Such a challenge would instantly become the most-watched congressional primary in the state, and likely the country, a generational battle between two well-liked members of the Democratic establishment. Markey, a Malden native elected to the Senate in 2013, has been a fixture of Massachusetts politics since he first won a House seat in the suburbs north of Boston in 1976, running as a political rebel unafraid to take on the Democratic establishment.
More: Majority of Mass. members of Congress backing Ed Markey’s reelection bid
“If Joe Kennedy got into the race, he would be the front-runner automatically, and Ed Markey would be faced with the most difficult race of his life,” said Mary Anne Marsh, a Democratic consultant based in Boston.
Markey has been building his reelection campaign — he had a sizable war chest of $4 million in cash on hand as of June 30.
“Senator Markey is running for reelection no matter who enters the race,’’ spokeswoman Giselle Barry said Saturday. “He is crisscrossing the state and will continue campaigning hard.”
Markey has collected endorsements from several members of the state’s congressional delegation, including Senator Elizabeth Warren, who has made a video supporting him, according to one person familiar with it. But there are notable holdouts, including Pressley and Representative Katherine Clark, a member of House Democratic leadership who is close with Kennedy. The news that Kennedy was weighing a primary challenge was first reported Saturday by The New York Times.
Markey’s hold on the Senate seat has been the subject of talk among Massachusetts political insiders after Pressley’s 2018 upset of Michael Capuano, a 10-term incumbent with a well-established liberal record, showed Massachusetts voters were open to primary challengers who make a compelling argument.
That speculation kicked into high-gear after Politico this week reported on telephone poll testing Kennedy against Markey. A citizen group has also launched an effort to draft Kennedy into the race.
But a primary challenge would surprise some Democrats who know Kennedy as a loyal and patient team player during his six years in Congress.
Former representative Barney Frank, a Democrat who was succeeded by Kennedy, said challenging Markey would seem out of character.
“Because he’s a very effective, highly regarded member who works well with other members, it would be totally inconsistent with his mode of politics,” Frank said.
And Frank did not sound warm to the prospect. “The idea that tens of millions of dollars would be spent on Democrats fighting other Democrats who have virtually no policy differences is crazy,” he said.
But Kennedy has been elevating his national profile. Democratic leaders chose him to give the party’s rebuttal to President Trump’s State of the Union address in 2018. During the midterms later that year, he traveled widely to campaign for other Democrats, and he frequently pens op-eds about his political beliefs on issues including foreign policy, mental health treatment, and legalizing marijuana.
Challenging Markey could be preferable to waiting for a Senate seat to open up — a development which could draw other high-profile contenders. Kennedy had $4.2 million in his campaign account as of June 30 and is known as an effective fund-raiser.
A group of Massachusetts Democrats is actively urging Kennedy to run, launching a website, Facebook group, and, just recently, an online petition that has about 200 signatures so far.
“We launched this effort not because we are anti-Markey, but because we strongly believe in Congressman Kennedy and his vision for America. These are unusual times in our nation and a new era in politics in which incumbency no longer means that someone is entitled to elected office in perpetuity,” said the draft movement’s organizers in an op-ed published in Commonwealth Magazine.
“In our view, we need passionate, proactive leadership in the US Senate to combat the divisiveness of Senate Majority Leader Mitch McConnell and the Republican Party. We need Joe Kennedy.”
The Massachusetts delegation’s longest-serving member, Markey already faces two primary challengers, though neither is well-known: Shannon Liss-Riordan, a labor attorney, and Steve Pemberton, a former foster child who became an executive and author.
With all the interest in his seat, Markey has been circling the wagons, lining up high-profile endorsements from major interest groups, including NARAL Pro-Choice America, a group that supports abortion rights; raising money; and spending on social media ads. Markey also has teamed with Ocasio-Cortez on legislation for her Green New Deal proposal to fight climate change, an issue he has been active on for years.
Markey’s vulnerabilities stem from his decades-long tenure in Congress, plus the fact that he is not as well known as some of his other colleagues, such as Warren, said Peter Ubertaccio, a political science professor at Stonehill College.
“I think he [Kennedy] and a number of other Democrats believe that Senator Markey has some vulnerabilities. And given some of the generational politics that we have seen playing out over the last few years, it doesn’t surprise me that there would be a challenge to Markey,” Ubertaccio said.
Liz Goodwin and James Pindell of the Globe staff and Globe correspondent John Hilliard contributed to this story. Jess Bidgood can be reached at Jess.Bidgood@globe.com. Follow her on Twitter @jessbidgood. Victoria McGrane can be reached email@example.com. Follow her on Twitter @vgmac.