Massachusetts Rep. Joe Kennedy III wrote today that he hasn’t made up his mind about running for the Senate in 2020, but he has filed documents with campaign finance regulators indicating that he is serious about a possible bid. 

Kennedy filed a statement of candidacy with the Federal Election Commission on Monday, which could set up a Democratic primary race against Sen. Ed Markey. But, also Monday, Kennedy posted a statement to Facebook saying he had not reached a decision about the race yet. 

[Rep. Joe Kennedy III, once staunchly anti-marijuana, changes his position]

“I am humbled by the words and actions of so many people supporting my potential candidacy. It means the world,” Kennedy wrote in the post. “I plan to spend the next couple weeks talking to as many of you as I can, trying to figure out if this campaign is right for me and right for Massachusetts.

Though Kennedy has one of the most well-known last names in Democratic politics, he faces an uphill climb.  

Markey has already fielded the support of the party establishment, and has endorsements from a majority of the Massachusetts delegation.

Markey also has backing from high-profile progressive groups, such as the Sunrise Movement, which has mobilized protests on Capitol Hill in support of the so-called Green New Deal. The sweeping plan to decarbonize the economy in order to stave off climate catastrophe is championed by progressive star Rep. Alexandria Ocasio-Cortez.

Markey, a sponsor of the Green New Deal, invited Sunrise Movement co-founder Varshini Prakash to the State of the Union address earlier this year.

The race diverges from the typical Democratic primary story where a progressive challenges a centrist party stalwart. 

“Kennedy is not himself on the left edge of the Democratic party and Markey’s vulnerability, to the extent he is vulnerable, is not that he is not liberal enough,” said David A. Hopkins, an associate professor of Political Science at Boston College. 

Markey’s vulnerability instead might be that he is lesser known than the state’s other senator, presidential candidate Elizabeth Warren. Warren has endorsed Markey.

Kennedy is likely to attack Markey from a generational standpoint — ripping a page out of the family playbook — not launch a challenge from the left flank.  

Kennedy, a fourth-term congressman, has made headlines for his ambitions for higher office before. Reportedly in preparation for a possible presidential campaign — he publicly declared his political vision to be “moral capitalism” in a high-profile speech.

Kennedy, who was once a staunch opponent to legalizing marijuana, changed course in 2018, endorsing nationwide legalization in a Boston Globe editorial.

A primary challenge, even an unsuccessful one, could raise Kennedy’s profile and make him a stronger candidate for the Senate should Warren resign for the presidency. 

“There are other ambitious folks around the state, Seth Moulton for instance, who may be interested in being a senator,” Hopkins said. “If Kennedy doesn’t see himself in the House long term and has greater ambitions, he wants to be part of the conversation. And he has done that in this current set of developments.”