PORTLAND, Maine (AP) — Republican U.S. Sen. Susan Collins and her Democratic opponent Sara Gideon sparred on health care and the nation's coronavirus response during a Thursday debate that saw the two candidates heavily criticize each other's records in office.

Collins, a 24-year senator, and Gideon, the speaker of the Maine House of Representatives, are in a heated, expensive race that could help determine control of the U.S. Senate.

Both candidates were on the offensive Thursday, with Collins criticizing Gideon for the Maine Legislature's failure to meet since March and Gideon portraying Collins as beholden to Republican President Donald Trump and Senate Majority Leader Mitch McConnell.

“The legislature has been out of session since March, and she has done nothing,” Collins said after touting her own work in support of the Paycheck Protection Program.

Gideon responded that Maine has a lower rate of coronavirus cases than most of the country and the state's economy hasn't suffered as much as others.

“Neither of those things is an accident," Gideon said. “That’s in direct contrast to the lack of leadership from the federal government. I am proud of us coming together.”

Gideon also charged Collins with jeopardizing the Affordable Care Act and touted the possibility of a public option for health coverage. Collins described a public option as a “first step toward a government takeover of our healthcare.”

Independent candidates Max Linn and Lisa Savage also participated in the debate. Savage, a Maine Green Independent Party member running as an independent, advocated for “Medicare For All” and bold climate action during the debate.

Linn, a conservative activist, portrayed himself as an outsider not beholden to political parties. His behavior attracted attention in previous debates in which he cut up a mask in protest of coronavirus-inspired facial covering requirements and used profanity on air.

“They're the faceplates of the Republican and Democratic establishment,” Linn said of Collins and Gideon on Thursday.

Maine Public hosted Thursday's debate, which was the third featuring the four candidates. The race is one of a handful of pivotal contests — including others in Iowa, North Carolina, Arizona and elsewhere — that are likely to decide control of the Senate. It's also the most expensive race in Maine's history, with Collins and Gideon raising more than $40 million between them.

The tight race with Gideon is an unfamiliar position for Collins, who has typically cruised to reelection in previous bids. Democrats and liberal groups mounted a campaign to unseat Collins after her vote to confirm Justice Brett Kavanaugh to the Supreme Court in 2018.

Linn and Savage are longshot candidates, but they could factor heavily in the outcome because of ranked choice voting. Because voters can rank all four candidates, second and third choices could come into play if no candidate cracks 50% of the total votes cast. Most polls show a close race between Collins and Gideon, so it's possible the ranked votes could make a difference.

Maine is the only state in the U.S. that uses the voting method to elect U.S. senators.

Thursday's debate did not include opening or closing statements from the candidates. It also had to compete with presidential town hall events featuring former Vice President Joe Biden and President Donald Trump.