Sen. Tom Udall (D-NM) announced he won’t seek reelection on Monday, opening up a seat in the Democratic-leaning state and thinning a bipartisan political dynasty that stretches back more than a century.

“The worst thing anyone in public office can do is believe the office belongs to them, rather than to the people they represent. That’s why I’m announcing today that I won’t be seeking re-election next year,” Udall said in a statement announcing his decision.

Udall served in the Senate for two terms, and before that was a House member going back to 1998. He spent his career focused on energy and conservation topics, critical issues for his home state, and was a leading voice pushing for renewable energy.

Udall’s seat will likely stay in Democratic hands, barring catastrophe. New Mexico has gone from being a swing state to safely Democratic in the last two decades. Potential Democratic candidates include Rep. Ben Ray Lujan (D-NM), though he may stick around the House since he’s in leadership, as well as freshman Reps. Xochitl Torres-Small (D-NM) and Debra Haaland (D-NM).

Udall’s retirement will also open up a spot on the powerful Senate Appropriations Committee.

Udall is part of a sprawling Mormon family dynasty occasionally called “The Kennedys of the West.” His cousin Mark Udall served one term in the Senate before losing to Sen. Cory Gardner (R-CO) in 2014. Their other cousin, Sen. Gordon Smith (R-OR), was a senator from 1997 through 2008.

Udall’s father Stewart was a congressman and U.S. Interior Secretary during the Kennedy and Johnson administrations, while his uncle Mo was a congressman and top presidential candidate in 1976. Udalls have held elected office every generation since Udall’s great-grandfather was elected to the New Mexico state legislature in 1898.

Congress won’t be left without Udall blood after 2020, however: Sen. Mike Lee (R-UT) is a second cousin of Tom’s.

This story was updated at 12:15 p.m.