U.S. Sen. Michael Bennet on Friday endorsed fellow Colorado Democrat Brittany Pettersen’s bid in the 7th Congressional District, all but sealing the Lakewood state senator’s path to the nomination.

Pettersen, who was first elected to the legislature in 2013, is the only prominent Democrat running for the seat held by eight-term U.S. Rep. Ed Perlmutter, the Arvada Democrat who announced earlier this month that he won’t run for re-election.

“I first met Brittany Pettersen when she was working on my campaign in 2010, and she has been part of the Bennet family ever since,” Bennet said in a statement. “You will be hard-pressed to find someone who cares more and works harder than Brittany. She has the life experiences and perspectives that are desperately needed in Washington. I know Brittany has what it takes to win this election and fight for the people of Colorado’s seventh district in the US House of Representatives.”

It’s the first time Bennet has made an endorsement in a primary for a U.S. House seat, a spokesman told Colorado Politics.

Perlmutter threw his support behind Pettersen on Thursday, days after two other potential Democratic candidates – Jefferson County Commissioner Lesley Dahlkemper and state Rep. Brianna Titone – announced that they aren’t going to run in the primary.

Pettersen said in a statement that she was honored to have an endorsement from Bennet, who is seeking a third term in November.

“His campaign in 2010 taught me what it takes to win tough races, and that experience has helped me succeed over the last 10 years,” she said. “He has been a mentor and someone I am lucky to call a friend. I’m excited that we get to campaign together once again, but this time we are both going to Washington when it’s done.”

Four Republicans are running in a primary for the seat, which is considered more competitive than it has been in the last decade under new boundaries approved last year by the state’s independent redistricting commission: Army veteran and first-time candidate Erik Aadland; former legislative candidate Laurel Imer, Golden economist Tim Reichert and Teller County resident Carl E. Andersen.

Democrats Kyle Faust and Julius Mopper, both first-time candidates, have also filed to run in the district.

The newly configured district encompasses Broomfield, Jefferson County and six sparsely populated mountain counties south and west of the metro area. Its voters have demonstrated a roughly 7-point lean toward Democrats in recent statewide elections, according to an analysis by the redistricting commission.

Colorado’s primary election is June 28.