PORTLAND (AP) — Independent U.S. Sen. Angus King, who caucuses with Democrats and once considered Susan Collins a political foe, is endorsing his Republican colleague’s bid for a fourth term in the Senate, her campaign says.

The two were to appear together today at the Margaret Chase Smith Library in Skowhegan.

King has not previously endorsed Collins, and they were political opponents when he beat her and Democrat Joe Brennan in a three-way race for governor in 1994.

But the two have worked well together in Congress. They created a “Gang of 14” to deal with the government shutdown, worked together on a student loan bill and combined their muscle to ensure that the Navy exercised an option to build an extra destroyer at Bath Iron Works.

“I think she’s one of the Senate’s MVPs — smart, tough and always willing to listen. In my book, she’s a model senator and I’m delighted to support her re-election,” King told The Associated Press in a statement.

Collins is being challenged by a political newcomer, Democrat Shenna Bellows, the former executive director of the Maine Civil Liberties Union.

King, a former Democrat, said he was going to Washington to try to break political gridlock.

And Collins, one of only two congressional Republicans left in New England, has shown a willingness to work with lawmakers from both parties over the years.

During the government shutdown, the two joined forces with a “Common Sense Coalition” to press for a compromise to end the stalemate, reopen government and avert a Treasury default.

King praised Collins for attempting to forge a compromise despite the possibility that she could come under attack by tea party activists, as was former Sen. Olympia Snowe, another moderate Republican from Maine who retired because of what she called corrosive partisanship that left the Senate at a stalemate.

“Since entering the Senate, I have had a chance to work with Susan Collins on a wide variety of issues. I’ve seen firsthand her work ethic, her intelligence and her integrity,” King said. “She always puts Maine and the country first and isn’t afraid to cross party lines to get things done.”

Collins, who faces write-in candidate Erick Bennett on the June 10 primary ballot, recently began stepping up her fundraising. In the last reporting period, she raised $870,000 and had more than $3.6 million in cash on hand. Bellows had $515,724 in cash on hand at the end of the reporting period on March 31.

The location chosen for today’s endorsement holds symbolic value for Collins. Collins has said Smith, the late senator who hailed from Skowhegan, was a mentor who inspired her.