Rep. Ben Ray Luján (D) on Monday said he would run for an open Senate seat in New Mexico, making him the first Democrat to formally enter the race to succeed retiring Sen. Tom Udall (D).

Luján, the No. 4 Democrat in House leadership, becomes an instant front-runner for the seat. He built a national donor base as chairman of the Democratic Congressional Campaign Committee, where he helped his party reclaim control of the House in the 2018 midterm elections.

"To move forward, we've got to fix the Senate, where Mitch McConnell stands in the way of progress," Luján said in a video posted to his Twitter account Monday, referring to the Senate majority leader.

His early announcement may help keep some candidates out of the race - state Attorney General Hector Balderas (D) has already said he will not run.

But others are eyeing the race, too, including Secretary of State Maggie Toulouse Oliver (D) and Rep. Deb Haaland (D), who said last week she is still thinking about running. A senior New Mexico Democrat said Oliver was openly speculating about a bid late last week, just after Udall said he would not seek a third term.

New Mexico, once a swing state, has turned reliably blue in recent years. No Republican has won a Senate seat there since Sen. Pete Domenici (R) won reelection in 2002, and Democratic presidential nominee Hillary Clinton carried the state by 8 percentage points in 2016.