GARDINER — Betsy Sweet, a longtime progressive activist and State House lobbyist who made an unsuccessful bid for the governor’s office in 2018, has announced that she will run for the U.S. Senate in 2020.

“It’s time to come together and unite around our values to create a government that works for the good of us,” Sweet told supporters at Sebago Lake Distillery in Gardiner. “Mainers care about each other. That’s who we are. That’s what we do.”

Sweet is the second Democrat to announce a run against Republican Sen. Susan Collins, a four-term incumbent who has yet to confirm that she’s running for re-election, even though she has already raised about $3.8 million, according to federal campaign finance records.

Sweet finished third in a seven-way Democratic primary for the governor’s office in 2018 that was determined by Maine’s new ranked-choice voting law. She was one of only three candidates in the 2018 primary to use public financing for her campaign.

Some pundits believe Collins, who has been increasingly targeted by Maine Democrats and progressive groups for voting to confirm U.S. Supreme Court Justice Brett Kavanaugh, is vulnerable in 2020. Collins is seen to have lost the support of moderate Democrats and equal rights activists over her Kavanaugh vote.

In her campaign announcement Thursday, Sweet said Kavanaugh’s confirmation and the passage of restrictive new abortion laws in Georgia, Alabama and Missouri have put the landmark Roe v. Wade  Supreme Court abortion ruling “under the greatest threat in a generation.”

She noted that at least one poll showed public support for Collins, who has been in the Senate since 1997, fell from 58 percent to 41 percent – an all-time low – and linked it to Collins’ vote to confirm Kavanaugh.

But Collins still appears to enjoy broad support among a cross-section of Maine voters. She had a high favorability rating in a recent Pan-Atlantic poll of 500 voters in March. That poll found 62 percent saying they had a favorable opinion of Collins. Sen. Angus King, an independent, had a favorable rating of 66 percent.

The poll, which had a 4.4 percent margin of error and a 95 percent confidence level, found that 51 percent of voters would choose Collins in a race against Maine House Speaker Sara Gideon, a Freeport Democrat. Although Gideon has not said she will run, her name has been among those mentioned as possible opponents to Collins from the left.

The poll found that 29 percent would pick Gideon, while 11 percent said they would select a third-party candidate and another 7 percent were undecided.

The National Republican Senatorial Committee reacted quickly to Sweet’s announcement, touting Collins’ record of bipartisanship.

“Meanwhile, lobbyist Betsy Sweet is a radical left-wing activist committed to making the loony policy dreams of Nancy Pelosi a reality,” the committee said in a prepared statement.

So far, only one other Democrat, Bre Kidman, a Saco attorney, has announced a run for Collins’ seat. Collins could also face a Republican challenger in a primary next June.

Derek Lavasseur, a Fairfield Republican, has said he will challenge Collins in a primary and has registered as a candidate with the Federal Elections Commission, but has not reported raising any campaign contributions.