Updated 11:44 a.m. | Rep. Ben Ray Luján plans to run for the Senate in New Mexico and is set to officially announce his candidacy Monday, according to two sources familiar with the Democrat’s decision.

The seat opened after Democratic incumbent Tom Udall announced Monday he would not seek re-election.

Luján, the assistant speaker and former chairman of the Democratic Congressional Campaign Committee, will be a formidable candidate. But he also isn’t likely to have the field to himself.

Rep. Deb Haaland and New Mexico Secretary of State Maggie Toulouse Oliver have been mentioned as potential candidates.

Toulouse Oliver tweeted Thursday that she was “seriously considering” a Senate run and would announce her decision “in the days ahead.”