U.S. Rep. Joe Kennedy III, a grandson of Robert F. Kennedy, is taking steps to challenge Sen. Edward Markey in the 2020 Democratic primary in what would be a rare, serious challenge to an incumbent.

Kennedy, 38, filed a statement of candidacy with the Federal Election Commission on Monday, though in a Facebook post he stopped short of formally declaring a run and said he will take several factors into account, including his young family.

�I am humbled by the words and actions of so many people supporting my potential candidacy. It means the world,� the congressman wrote. �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.�

He added that while some people have told him he should wait his turn, �I�m not sure this is a moment for waiting.�

Kennedy is in his fourth term in the House and had previously indicated plans to seek reelection next year.

Markey, 73, is running for a second full term in the Senate after serving for more than three decades in the House.

Two of Kennedy�s great-uncles, John F. Kennedy and Edward M. Kennedy, served as senators from Massachusetts.

(AP)