In the ad, an Ogunquit lobsterman says he voted for Collins in the past but that the tax bill she voted for “didn’t help regular Mainers.”

"The number one thing we hear from Mainers about Senator Collins is how disappointed they are in her vote on the tax bill. They think the tax bill was a windfall for her special interest donors and didn’t do anything for average Mainers — and they are right,” said Willy Ritch, a spokesman for Maine Momentum.

Kevin Kelley, a spokesman for the Collins campaign, dinged Maine Momentum as “a dark money group that refuses to disclose its donors and that the Washington Post’s independent fact-checker has already said has a history of making false claims.”

“I doubt that misleading and untruthful political ads are on any Mainers’ holiday wish list,” Kelley said. “The truth is nearly 9 out of 10 Maine families who owe federal income taxes received a tax cut.”

The massive ad buy will go far in Maine, a state with a relatively cheap media market. But it’s also got plenty of competition: The state has now seen $7 million in spending for TV, radio and digital ads for a race that’s almost certain to be the most expensive in the state’s history. At this early stage, it’s the most expensive Senate race in the country.

Currently, the edge in spending goes to Democrats. With this buy, Maine Momentum will near $2 million in spending, nearly matching Gideon’s $2 million in ad buys, while Majority Forward spent more than $200,000 just this week and is over $750,000.

Collins has spent more than $1 million and her biggest outside backers, 1820 PAC and the U.S. Chamber of Commerce, have each put in more than $500,000, according to media statistics.

James Arkin contributed to this report.