“WASHINGTON — Sara Gideon, the speaker of the Maine House of Representatives, on Tuesday formally became the Democratic nominee to challenge Senator Susan Collins of Maine, wielding a formidable war chest in a race that could determine whether Republicans retain control of the Senate in November.
Ms. Gideon, backed by the Senate Democratic campaign arm and a number of outside political groups, had long been the favorite to challenge Ms. Collins, the sole remaining New England Republican in Congress. The nonpartisan Cook Political Report has rated the race a tossup, and the election has already become the most expensive in Maine history.
“This campaign is about all of us, and about how we can build a stronger future together,” Ms. Gideon said in an acceptance speech broadcast on Facebook. “After 24 years in Washington, Senator Collins has become part of that broken system, putting special interests and her political party first, and Mainers know it and feel it.”