Gov. Janet Mills announced her endorsement of Democratic nominee Sara Gideon in Maine’s U.S. Senate race Thursday.

The endorsement from Mills, also a Democrat, comes two days after Gideon overwhelmingly won the party’s nomination to challenge Republican Sen. Susan Collins in November.

“Sara Gideon has a proven track record of standing up for Maine families no matter what, and I’m proud to endorse her in this race,” Mills said in a statement put out by the Gideon campaign.

“From her leadership on protecting Mainers with pre-existing conditions to passing legislation to lift Maine children and families out of poverty, she brings people from all parties together to make real progress on the issues that matter. Sara is a tireless advocate for Maine people and I know she will never stop fighting for us in the U.S. Senate.”

Democrat U.S. Rep. Chellie Pingree also endorsed Gideon on Thursday, saying in a statement that Gideon “knows how to bring people together to make progress on every issue from health care to climate change for the benefit of all Maine people. I’m proud to endorse Sara in her campaign, and know she will be a fantastic senator who will fight tirelessly for our people and state.”

Gideon, who serves as Maine’s speaker of the House, will challenge Collins in what is already the most expensive race in state history, and which has drawn national interest because it could help determine which party controls the Senate.

On Wednesday, the Human Rights Campaign, an LGBTQ rights advocacy organization that endorsed Collins in previous races, also announced it would endorse Gideon, citing Collins’ support of U.S. Supreme Court Justice Brett Kavanaugh and a failure to hold Donald Trump accountable.