Senator Tom Udall of New Mexico announced on Monday that he will not seek reelection in 2020. He offered no specific explanation for his decision, saying merely that, “the worst thing anyone in public office can do is believe the office belongs to them, rather than to the people they represent.” Originally elected in 2008, he’s only seventy years old and in seemingly good health. His decision will make it incrementally more difficult for the Democrats to retake control of the U.S. Senate in 2021.

His father Stewart Udall was the environmentally conscious and conservation-minded Secretary of the Interior throughout the 1960’s, and Tom has been bringing that same sensibility to his job in Congress. He’s the ranking member on the Appropriations Subcommittee on Interior, Environment, and Related Agencies, which gives him a lot of influence over how money is spent to protect our land and resources and combat climate change and pollution. His absence will be felt immediately even if the Democrats hold his seat.

There’s reason for optimism on that front, as New Mexico has been trending hard in the Democrats’ direction in recent years. The party won every statewide office on the ballot in the 2018 midterms and has a Democratic governor, two Democratic senators, and an all-Democratic caucus in the House. By way of caution, it should be remembered that George W. Bush carried the state in 2004 by a razor-thin 49.8 percent to 49.0 percent advantage.

Immediate successors mentioned to replace Udall from the Democratic side include all three members of Congress (freshmen Deb Haaland and Xochitl Torres Small, as well as DCCC chairman Ben Ray Luj├ín) and the state’s attorney general, Hector Balderas. Perhaps because this news came as a surprise, there are no people lined up for the GOP with statements or intentions to run.

It’s almost always easier to flip a Senate seat if it’s open rather than occupied by an incumbent, and that’s certainly true here because Tom Udall is popular and not plagued by any whiff of scandal. Donald Trump lost the state in 2016 to Hillary Clinton by 8.3 percentage points, carrying only 40 percent of the vote. If he can’t improve on that performance dramatically, he’ll serve as a drag on the ticket. Still, this is welcome news for the GOP because it at least gives them a shot a making a pickup, and they’re probably worried that they’ll lose at least a couple of seats in 2020 if things don’t improve for them between now and then.

Regardless of what happens to the seat, I’m sorry to learn that Udall won’t be staying in the Senate fighting for environmental causes from his powerful perch on the Appropriations Committee. He won’t be easy to replace.