Maine House Speaker Sara Gideon, D-Freeport, takes the oath of office in Augusta. Dec. 5, 2018.

AUGUSTA, Maine — Maine House Speaker Sara Gideon announced a 2020 run against U.S. Sen. Susan Collins in a long-expected campaign launch on Monday that made her the second well-known Democrat to challenge the Republican incumbent.

Gideon, 47, of Freeport first teased a run against Collins immediately after the Republican voted in November for U.S. Supreme Court Justice Brett Kavanaugh. That vote kicked off a period of unprecedented partisan mobilization for and against the four-term senator.

Two progressive crowdfunds have raised nearly $4.7 million for Collins’ eventual Democratic challenger, but Collins virtually matched them with $4.4 million as of March’s end behind a record fundraising quarter after the Kavanaugh vote on the backs of large, out-of-state donors.

In her launch video, Gideon hit Collins for two landmark votes during the presidency of Donald Trump: the one for Kavanaugh and the other for the Republican tax-cut package passed in 2017, saying “at one point, maybe she was different than some of the other folks in Washington, but she doesn’t seem that way anymore.”

The House speaker is a Rhode Island native who moved to Maine in 2004. She was a Freeport town councilor before winning her leadership position during her third House term in 2016.

In the Legislature, she has backed efforts to expand access to an opioid overdose antidote and align aid programs with workforce training. A core message of her campaign emerged on Monday, when Gideon contrasted consensus work in the Maine Legislature — which must pass bipartisan budgets — with relative inaction in Congress.

“In the State House and even on the Freeport Town Council, I realized that I know how to bring people together,” Gideon said in an interview.

After a Democratic wave election in 2018, Gideon sponsored a successful bill to establish automatic voter registration in Maine. On Monday, the Maine Republican Party flagged her support of a failed Democratic effort to institute a carbon tax and Senate Republicans’ campaign arm called Gideon “an extreme partisan.”

It may be an uphill battle to unseat Collins, who has won re-election by increasing margins since her first race in 1996. In a March poll from Pan Atlantic Research that tested Collins against Gideon, the incumbent got 51 percent support to the Democrat’s 29 percent, though two-fifths of Mainers didn’t know enough about Gideon to rate her approval.

Collins has been ranked by VoteView as the most moderate Republican senator since Maine’s Olympia Snowe left the Senate in 2013, though Democrats have questioned how much that label means in a gridlocked Congress where little legislation is moving. She also cast a pivotal 2017 vote against a Republican plan to repeal the Affordable Care Act.

Gideon joins lobbyist Betsy Sweet of Hallowell, the third-place finisher in the 2018 Democratic gubernatorial primary, in the party field alongside little-known Saco lawyer Bre Kidman. Other Democrats are considering a run, including Secretary of State Matt Dunlap of Old Town and developer Rosa Scarcelli of Portland.

In a statement, Collins spokesman Kevin Kelley didn’t directly address Gideon, saying Democrats have a “competitive primary” ahead of them and saying the incumbent will “continue to build on her record of extraordinary accomplishments.”

Sweet has hinted at a run to Gideon’s left, saying earlier this month that the stylistic differences between the House speaker and her would be “moderate, around-the-edges approaches to try to fix things” versus “bold and courageous action.”

Watch: Susan Collins, the last Republican in Maine’s congressional delegation, talks about need for bipartisanship

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Michael Shepherd joined the Bangor Daily News in 2015 after time at the Kennebec Journal. He lives in Augusta, graduated from the University of Maine in 2012 and has a master's degree from the University...