FALL RIVER, Mass. (WPRI) — Congressman Joe Kennedy III will decide in the coming weeks whether to mount a Democratic primary challenge next year against incumbent Sen. Ed Markey, WPRI 12 has confirmed.

A person close to Kennedy said the four-term House lawmaker, 38, is serious about a possible Senate run — a move that would represent a political earthquake in Massachusetts — and currently weighing what to do. (Kennedy was spotted on Nantucket over the weekend.)

Markey, 73, has represented Massachusetts in Congress since 1976, initially in the House. He won his Senate seat in a 2013 special election following John Kerry’s appointment as secretary of state. Paul Tencher, a senior adviser to Markey, says Markey is prepared to wage a primary fight against Kennedy to hold onto his seat.

Markey’s campaign on Monday released a pre-taped endorsement video by U.S. Sen. Elizabeth Warren backing the senator. “We need Ed Markey in the Senate now more than ever,” she said in the video. “And here’s why. Because he’s a leader. He’s a fighter. And he is a true progressive.”

A June poll by Suffolk University found only 39% of Massachusetts voters had a favorable opinion of Markey, while 25% viewed him unfavorably and 36% either hadn’t heard of him or had no opinion.

Jennifer Duffy, who analyzes U.S. Senate races for the nonpartisan Cook Political Report in Washington, said Kennedy’s flirtation with a run “doesn’t make a lot of sense to me.”

“Challenging a Senate incumbent is quite different than challenging a House incumbent,” Duffy told WPRI 12, recalling Rhode Island Republican Steve Laffey’s unsuccessful primary run against then-U.S. Sen. Lincoln Chafee in 2006.

“The party will back Markey,” she said. “It could prove to be a very expensive and ugly race. However, it seems to me that Kennedy is smarter than to go down that path. It could derail what could be a very long political career.”

Joe Kennedy III is the grandson of Robert F. Kennedy, whose siblings included President John F. Kennedy and the late Sen. Ted Kennedy. Joe Kennedy III’s father is former Congressman Joe Kennedy II.

Former New Bedford Mayor Scott Lang, who has been flirting with a primary challenge against Markey for months, said Monday he plans to decide whether to run after Labor Day.

“The fact is, he just needs to be a better senator if he’s going to win,” Lang told WPRI 12, arguing Markey was spending too much time on issues like the Green New Deal rather than efforts to “bring home the bacon” for cities like New Bedford.

Lang, who worked on Ted Kennedy’s 1980 presidential campaign, said he has “tremendous admiration” for Joe Kennedy, though he said his own decision would not be affected by the congressman’s.

“I believe that Kennedy is a progressive centrist, and that’s where I believe this Senate seat needs to be,” he said.

If Kennedy runs for Senate, there would be a domino effect locally: it would create an open race for his current 4th District House seat, which runs along the Rhode Island border from northern Fall River through the Attleboros up to the Boston suburbs.

Politico Massachusetts reported Monday that other potential 4th District candidates would include Treasurer Deb Goldberg, the Alliance for Business Leadership’s Jesse Mermell and Newton City Councilor Jake Auchincloss. One candidate, Ihssane Leckey, has already filed to run against Kennedy.

State Sen. Paul Feeney, D-Foxboro, confirmed Tuesday he would be a potential candidate for the 4th District U.S. House seat if Kennedy runs for Senate, though he emphasized that at the moment he’s running for another term on Beacon Hill.

“There is no open seat for Congress at this point, so I’m truly reluctant to give it too much thought,” Feeney told WPRI 12 in an email. “However if the congressional seat were to open up, I would certainly take a serious look at it and discuss it with my family and supporters.”

“I’m humbled by those that have reached out in the last couple of days to urge me to run if the opportunity presents itself, and I will give it serious consideration at the right time, but right now I will continue to focus on the work I’ve been elected to do,” he added.

In the 2016 election, the last time Kennedy faced a Republican challenger, half the ballots cast for U.S. House came from just nine of the 34 communities in the 4th District: Newton (12%), Brookline (7.5%), Taunton (6%), Attleboro (5%), Needham (5%), Franklin (5%), North Attleboro (4%), Wellesley (4%) and Milford (3.5%).

Massachusetts’ 4th Congressional District is shown in purple. (credit: nationalmap.gov)

Ted Nesi (tnesi@wpri.com) is WPRI 12’s politics and business editor and a Target 12 investigative reporter. He is a weekly panelist on Newsmakers and hosts Executive Suite. Follow him on Twitter and Facebook