Republican Senate President Mike Thibodeau announced Tuesday morning that he is running for governor, setting up a June Republican primary that includes the Legislature’s top three Republicans, plus at least one other heavyweight.

Thibodeau, 51, of Winterport, told WVOM that, as of Tuesday morning, he is in. At the same time, his campaign issued a release announcing that he will join the GOP primary field that includes former Maine Health and Human Services Commissioner Mary Mayhew, House Minority Leader Ken Fredette and Senate Majority Leader Garrett Mason.

Shawn Moody, who ran for governor as an independent in 2010, joined the Republican Party earlier this month and is expected to announce his Blaine House bid in November.

“We, my wife and I, had to consider do we offer something unique? Is there something that sets us apart from the others?” Thibodeau said. “The answer, I think, is yes we do.”

Thibodeau, who has often found himself at odds with Republican Gov. Paul LePage during the past four years, is a business owner who is term-limited out of the Senate next year. He has worked closely with Mason during their four years as Republican leaders of the Maine Senate.

Unlike Mason, who has filed to run a publicly funded campaign, Thibodeau will fund his election bid with private funds. Fredette and Mayhew also filed to run privately funded campaigns.

Thibodeau was first elected to the Maine Senate as part of a conservative wave that placed LePage in the Blaine House and gave the GOP majorities in both chambers of the Legislature for the first time in more than three decades. He has won re-election three times in close races. He became Senate president at the start of his third term and has served in that role since.

As LePage and others in the Legislature created a more extreme image for the party, Thibodeau stood his ground, playing key roles in negotiating budgets that prevented a government shutdown in 2015 and minimized the damage of the one that happened earlier this year.

While he was elected to the Senate as a fiscal and social conservative, Thibodeau’s defense of the legislative process and refusal to cave to the governor’s pressure have shaped a more moderate public image. However, he said Tuesday that he never saw his actions as taking stands against LePage outright.

“It’s about getting things done. It’s not about blind loyalty,” he said. “It’s about passing the best public policy we can.”

His decision to announce came just three days after U.S. Sen Susan Collins revealed that she would not seek the Blaine House, a move that allows Thibodeau to claim the mantle of moderation, based on his personality, while still offering solid ideological bona fides to the conservative voters who are likely to decide the June primary. The fact that Kevin Raye, a moderate former Maine Senate president, and Bob Emrich, a conservative Christian, have agreed to co-chair his campaign reinforces his appeal to both major wings of the Maine Republican Party.

“We need to come together to rein in the growth of government not only to preserve Maine’s unique way of life, but to protect our freedoms,” he said in a prepared statement. “We need to continue to improve our economy, create more jobs, and educate our children so they can live and work here at home.”

Two independents, two Greens and 10 Democrats also have filed to run in 2018 to replace LePage, who cannot seek re-election because of Maine’s term limits law.

Christopher Cousins has worked as a journalist in Maine for more than 15 years and covered state government for numerous media organizations before joining the Bangor Daily News in 2009.