Massachusetts Rep. Joe Kennedy said he is considering a run for U.S. Senate next year in a Monday Facebook post.

In recent weeks, pro-Kennedy groups have encouraged the 38-year-old congressman to challenge Sen. Ed Markey in a Democratic primary. "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," Kennedy said in the post.

Kennedy comes from one of the most storied families in American politics. He is the grandson of Sen. Robert F. Kennedy and a grand-nephew of both President John F. Kennedy and Sen. Ted Kennedy. He has been in the House of Representatives since 2013, and delivered the official Democratic response to President Trump's State of the Union address in 2018.

Get Breaking News Delivered to Your Inbox

Markey has been in Congress since 1976 and a member of the Senate since 2013. He has been a leader on energy and environmental policy during his time in Congress and served on the House Select Committee on Energy Independence and Global Warming from 2007 to 2011.

Markey, who will be 74 on Election Day, has repeatedly said that he will run for reelection. He has already been endorsed by Sen. Elizabeth Warren and Boston Mayor Marty Walsh.

In an op-ed in Commonwealth Magazine, supporters of Kennedy said their desire for him to be a U.S. Senator has nothing to do with Markey.

The four authors of the piece, who have also organized a petition for a Kennedy Senate bid, wrote, "We launched this effort not because we are anti-Markey, but because we strongly believe in Congressman Kennedy and his vision for America."

When news first broke about Kennedy's potential run, the League of Conservation Voters endorsed Markey, calling him "one of the leading voices in the U.S. Senate for climate action."