PORTLAND, Maine (AP) — Maine voters did much of their work ahead of Tuesday's primary election, casting tens of thousands of absentee ballots as House Speaker Sara Gideon faced two other Democrats to challenge Republican U.S. Sen. Susan Collins in a race that’s critical to the battle for control of the Senate.

Because of the pandemic, state officials encouraged voters to use mail-in absentee ballots instead of voting in person to avoid crowds at polling places that could serve to spread the coronavirus.

Polling stations were open nonetheless on Tuesday with strict sanitation rules, but they were quiet and voters were scarce.

“This is crazy. I didn’t expect it to be this sparse. But touché for everyone who’s showing up,” voter Mark Tschamler said after departing what's normally a busy polling station in Portland.

Secretary of State Matthew Dunlap said voting had gone smoothly with nearly 200,000 absentee ballots. “Working with the clerks, we think we’ve done a pretty good job mapping this out,” he said.

In the Democratic Senate primary, Gideon faced challenges by activist Betsy Sweet and attorney Bre Kidman.

Gideon, who's raised a staggering $23 million, received early backing from the Democratic establishment, securing an endorsement from the Democratic Senatorial Campaign Committee, and has kept a laser focus on Collins, much to the chagrin of her challengers.

Kidman and Sweet criticized the Washington influence and said Gideon’s vow to take money out of politics rang hollow as her own money grew into the biggest haul for a political candidate in state history.

If no candidate receives 50% of the vote, then the outcome will be decided through an additional voting round in which the last-place candidate is eliminated and votes reallocated under Maine's ranked choice voting law. That process could take several days to wrap up.

The winner is entitled to about $3.7 million from a crowdsourced fund for Collins’ challenger that was established during the Senate fight over Brett Kavanaugh’s Supreme Court confirmation. Some Democrats were furious over Collins’ vote in favor of Kavanaugh, President Donald Trump’s controversial appointee.

Collins has raised $16 million. The four-term senator is a household name in the state with a reputation for independence, but Democrats are battering her over her critical 2018 support for Kavanaugh,

Democrats need to gain at least three seats to capture Senate control. Republicans are defending 25 of the 38 seats in play, even as Trump’s deteriorating standing in the polls jeopardizes GOP candidates around the country.

With Collins widely considered one of the GOP’s most endangered Senate incumbents, a Collins victory would narrow Democrats’ pathway to wresting control of the chamber.