This month, Ms. Gideon, who is widely favored to win the Democratic primary on Tuesday, announced that she had raised $9 million in the second fund-raising quarter of the year, three times what Ms. Collins announced in a preliminary report before the primary. Ms. Gideon, who also reported having $500,000 more cash on hand than Ms. Collins, is expecting another windfall after the primary: at least $3.5 million in funds raised during and after the confirmation of Justice Kavanaugh and tied to her helping confirm him, which Ms. Collins condemned as an attempted bribe aiming to sway her critical vote.

The quarantine restrictions imposed during the pandemic — including the cancellation of cherished annual events paying homage to a cornucopia of edible Maine bounties — mean that more families are most likely to be at home, consuming the negative advertisements against her. (The Senate Republican campaign arm has also unveiled a flurry of ads to bolster Ms. Collins, attacking Ms. Gideon as an ineffective politician.)

All of which has Ms. Collins concerned.

“I am,” she said as she finished a jumbo lobster roll with a sprinkle of lemon — no mayonnaise or butter — on the boat ride back to Eastport. “But in the end, I think people in the state know me really well.”