Gov. Janet Mills’ entrance into the U.S. Senate race on Tuesday immediately shook up the Democratic primary, prompting one of her competitors to drop out of the race.

Maine Beer Co. cofounder Dan Kleban said in a news release that he is suspending his campaign and endorsing Mills, calling her “the right leader for the right moment.”

“Right now, our country is at a crossroads,” Kleban said. “Susan Collins is not doing what’s right for the state of Maine, and hardworking Mainers are literally paying the price — housing, health care, groceries, and electric bills are all too high and getting worse.

“I believe Governor Mills will win next year and put Mainers first by addressing these pressing issues.”

A spokesperson for Collins’ campaign, meanwhile, projected confidence following Mills’ announcement and said the five-term Republican would be ready to take on whoever emerges as the Democratic candidate.

“We will be prepared to have a vigorous campaign against whoever wins this very chaotic Democratic primary,” Shawn Roderick said in a written statement.

Two of Mills’ leading Democratic competitors — Graham Platner and Jordan Wood, who have each raised millions — welcomed Mills to a race that is expected to be among the most closely watched anywhere in the country.

National political forecasters immediately moved the race from leaning Republican to a toss-up on Tuesday, and national powerhouse EMILYs List endorsed Mills, who has expanded and strengthened reproductive rights over her seven years as governor.

EMILYs List President Jessica Mackler highlighted Mills’ experience and trailblazing career as the first female district attorney in New England and first female attorney general and governor of Maine.

“This moment demands someone with backbone and grit,” Mackler said in a written statement. “Someone who has proven she will fight Trump head on and defeat him when he tries to hurt Maine — that is Janet Mills.”

Collins is the top target of Democrats in the 2026 midterms. She’s the only Republican representing a blue state on the ballot next fall and her favorability ratings are near or at historic lows.

Still, Collins has proven herself to be politically resilient, including in the 2020 race after she cast the deciding vote to confirm Brett Kavanaugh to the U.S. Supreme Court, which caused the end of national abortion protections under Roe v. Wade.

Despite trailing in the polls, Collins ended up winning by nearly 9 points, even though Democrat Joe Biden beat Republican Donald Trump by a similar margin.

Kyle Kondik, the managing editor for Sabato’s Crystal Ball at the University of Virginia Center for Politics, said in a social media post that they were reclassifying Maine from leaning Republican to a toss-up.

“It should be a Democratic-leaning year next year to at least some extent,” Kindik told the Press Herald. “Collins is formidable but is not as popular as she once was … (and) Democrats likely will have a reasonably strong challenger to her, either the newly-announced Mills or another Democrat who defeats Mills in the primary.”

The Cook Political Report, another leading election forecaster, also moved the race to a toss-up Tuesday.

“For the first time since she was elected in 1996, Collins could face off against a sitting statewide officeholder who, like her, has a proven track record of outperforming the presidential ticket of her party,” publisher and editor-in-chief Amy Walter wrote.

Mills was the top choice of national Democrats, including Senate Minority Leader Chuck Schumer, D-N.Y.

U.S. Sen. Catherine Cortez Masto, D-Nevada, said she’s supporting Mills, calling her a “proven leader who knows how to win in Maine.”

“When we served as attorneys general together, I saw how Janet Mills stands up for Maine — taking on the big banks and drug companies, keeping families safe, and always putting Mainers first,” she said in a social media post.

Unlike previous challengers, Mills, 77, will have to win a primary before taking on Collins. But the early endorsement from EMILY’s List will give the two-term governor an additional advantage over her lesser-known and more inexperienced challengers, who have never held elected office.

That primary also will spotlight the generational anxiety of the party nationally. Graham Platner, a 41-year-old oyster farmer and veteran, and Wood, a 36-year-old former Capitol Hill staffer, have both raised millions.

Platner has drawn the most excitement and largest crowds at town hall events across the state, including more than a thousand people in Portland and hundreds more at other events in rural parts of the state. His campaign has been highlighting letters to the editor urging Mills not to run. And U.S. Sen. Bernie Sanders, the Vermont independent and progressive standard-bearer who endorsed Platner, criticized national party leaders for encouraging Mills to run.

“It’s disappointing that some Democratic leaders are urging Gov. Mills to run,” Sanders said in a release. “We need to focus on winning that seat & not waste millions on an unnecessary & divisive primary.”

Platner was endorsed Tuesday by a network of young progressives, including Leaders We Deserve, which was co-founded by David Hogg, a gun safety advocate and former vice chair of the Democratic National Committee.

Republicans, meanwhile, are relishing what is currently a crowded Democratic primary. The Republican National Committee issued a statement titled, “Janet Mills creates messy Maine primary.”

“Janet Mills, Graham Planter, or whatever other leftist emerges from this Democrat primary will be too extreme and socialist for Maine,” regional spokesperson Delanie Bomar said in a written statement.

For her part, Mills told the Press Herald that a competitive primary is a “healthy process.” She beat six other Democrats to win the nomination for governor in 2018.

Both Platner and Wood welcomed Mills to the primary, while focusing their criticism on Collins.

“I have held over twenty town halls in every corner of Maine, from Rumford to Madawaska to Portland,” Platner said in a written statement. “Everywhere I hear the same thing: people are ready for change. They know the system is broken and they know that politicians who have been working in the system for years, like Susan Collins, are not going to fix it.”

Wood, who has been holding town hall events across the state since the spring, called for a series of debates — one in each county.

“Primaries are a vital part of the democratic process — they give Mainers the power to decide who will be the future leaders of our party and state,” Wood said. “To defeat Susan Collins, we need a Democratic candidate all Mainers can trust to serve and represent them, not special interests or party bosses.”