Rep. Joe Kennedy III (D-Mass.) said Monday that he is eyeing a run for the US Senate in 2020, a move that would set up a major Democratic primary fight against Sen. Ed Markey.

“Over the past few weeks I’ve begun to consider a run for the U.S. Senate. This isn’t a decision I’m approaching lightly and — to be completely candid — I wasn’t expecting to share my thoughts so soon,” Kennedy wrote in a Facebook post.

The 38-year-old congressman went on to write that he had not yet made a final decision, saying it would come in “the next couple weeks,” after “talking to as many [Massachusetts voters] as I can.”

Despite his hesitance to confirm his candidacy, Kennedy has already filed to run for a US Senate seat in Massachusetts with the Federal Election Commission, according to FEC records.

Kennedy made no mention in his post of Markey or a primary challenge.

“I hear the folks who say I should wait my turn, but with due respect — I’m not sure this is a moment for waiting. Our system has been letting down a lot of people for a long time, and we can’t fix it if we don’t challenge it,” Kennedy wrote, adding, “I’ve got some ideas on how to do that.”

Markey came to the Senate in 2013 following a 36-year career in the House of Representatives. He won a special election to serve the remainder of John Kerry’s term after Kerry was confirmed as secretary of state.

The 73-year-old is considered one of the most liberal voices in the Senate. He has been known for his record on environmental causes, acting as a leading sponsor of freshman Rep. Alexandria Ocasio-Cortez’s (D-NY) Green New Deal and serving as chair of the House Select Committee on Energy Independence and Global Warming.

Despite his record, however, Democrats in Massachusetts have begun to worry Markey could be vulnerable to a younger challenger, according to the Washington Post.

After rumors first emerged about a potential Kennedy challenge, Markey secured 2020 Democratic contender and fellow Massachusetts Sen. Elizabeth Warren’s endorsement, and has continued to state publicly that he has every intention of running in 2020.

Kennedy, meanwhile, was an early endorser of Warren’s 2020 campaign.

Regardless, Kennedy has slowly come into the political spotlight as the newest star in his family’s storied dynasty.

His father, Joseph P. Kennedy, also served in the House of Representatives. His grandfather was Sen. Robert F. Kennedy.

Whether Kennedy decides to go through with his Senate bid or not, Markey will still have two primary challengers to face.

Attorney Shannon Liss-Riordan and businessman Steve Pemberton have already filed to run for the seat as well.