Early spending on Maine’s U.S. Senate race is the fourth highest in the country, according to AdImpact, a nonpartisan group that tracks political advertising expenditures.

So far, about $15.3 million has been spent to sway voters. Maine trails Senate races in Texas and Georgia, and the California governor’s race, where spending has reached $57.6 million, $26.1 million and $20.5 million, respectively.

The deluge of advertising money hitting Maine shows the importance of the Senate seat, currently held by Republican Sen. Susan Collins, in determining control of the chamber. Republicans currently hold a 53-47 majority.

For the second consecutive cycle, Democrats are bullish about toppling Collins, who suffers from low approval ratings. But Collins has defied expectations before, including in the 2020 race, which she won convincingly despite trailing in the polls against a well-funded opponent.

The 2020 race drew about $200 million in total spending, according to a study conducted by America Promise, which seeks to reduce the influence of money in politics. The race was the second most expensive per vote that cycle, a Press Herald analysis found.

Democrat Sara Gideon, a former Maine House speaker from Freeport, raised $75.6 million, compared to Collins’ $30 million. Gideon ended her campaign with about $12 million in leftover cash. She lost by nearly 9 points.

Earlier this year, Politico reported that the National Republican Senatorial Committee predicted that both parties combined would spend between $400 million and $600 million in Maine’s Senate race.

This cycle, Maine is home to one of six races with more than $10 million in spending, AdImpact said.

Republicans are currently spending more than their counterparts, but Maine and Georgia have the closest split. Republicans have a $2.8 million edge here, compared with a $2.6 million advantage in Georgia.

Michael Socolow, a communications and journalism professor at the University of Maine, said the early spending is driven by many factors, including the state’s relatively affordable advertising rates compared to larger markets and the overall competitiveness of the race.

“The more competitive the race, the more money is going to be put into it by both parties,” Socolow said. “If you look at the national map, picking out the really competitive places is getting harder and harder, and that’s why somebody’s coming into Maine.”

The candidate mix is also a factor, Socolow said. Collins is the chair of the Senate Appropriations Committee and consistently polls lower than she performs on Election Day. She’s the only Republican from New England left in Congress.

There’s also a competitive Democratic primary in June between two-term incumbent Gov. Janet Mills and political newcomer Graham Platner, a combat veteran and oyster farmer who has captivated progressives.

“That combination brings in a lot of national money,” Socolow said.