Republicans and their allies are spending nearly twice as much as their Democratic counterparts on advertising in the U.S. Senate race, putting them in a strong position to defend Republican U.S. Sen. Susan Collins in November.

Republican-aligned groups have spent more than $68 million on TV, radio, satellite and digital ads this cycle, compared to $37.6 million by Democratic-aligned groups, according to AdImpact, which tracks spending on political ads.

The spending advantage appears to be growing by the day. In April, Republican groups have spent or are scheduled to spend $4.1 million on ads, compared to less than $1 million by Democrats. And they hold a more than 2-to-1 advantage in scheduled ad spending leading up to the primary and the general elections.

The disparity shows that Republicans view Collins’ seat as crucial to winning the majority in the Senate.

Collins, 73, is considered the most vulnerable Senate Republican this cycle, given her historically low approval ratings. She’s the only one running in a state won by Democrats in the 2024 presidential election.

At the same time, Republicans are facing headwinds nationally, as President Donald Trump’s approval ratings have hit a second-term low in some surveys amid his widely unpopular bombing campaign in Iran.

The disparity also stems from a lack of spending by Gov. Janet Mills and her allies. Mills has no ads booked in the coming weeks, a potentially alarming sign for her campaign. Her allies in Washington, D.C., led by Senate Minority Leader Chuck Schumer, have also scheduled no ads to boost Mills.

Mills is fighting for her political life against political upstart Graham Platner. The 41-year-old oyster farmer is barnstorming the state and drawing large, enthusiastic crowds to town hall events.

Platner has a significant fundraising advantage, having raised $7.9 million through the end of last year to Mills’ $2.7 million. And he’s leading Mills by double digits in most independent polling.

He’s using that cash to fuel a spending blitz on ads, and Mills is having trouble keeping pace.

As Democrats duke it out, Republicans and their allies have been airing ads trying to build up Collin’s favorability ratings by highlighting funding she helped secure for hundreds of projects in Maine. These groups have spent or scheduled an astounding $67.8 million in pro-Collins ads, per AdImpact.

From the beginning of the race through Friday, no outside group spent more in Maine than One Nation. The 501c(4) dark money group has placed $13.9 million in ads touting Collins’ legislative accomplishments.

Collins, who leads the Senate Appropriations Committee, has secured $1.5 billion in federal earmarks, formally called congressional directed spending, for more than 670 projects throughout the state since being reelected in 2020.

Ads run by One Nation urge viewers to thank Collins for helping provide firefighters with safety equipment free of toxic forever chemicals; funding for advanced diagnostic equipment upgrades at rural hospitals; drinking and wastewater infrastructure investments; and medical research funding for cancer, diabetes and autism.

One ad, applauding Collins’ record on Social Security, features an offhand comment from Mills praising the Republican senator.

“I appreciate everything she is doing,” Mills says in a soundbite captured before she entered the race.

Stronger America, another 501c(4) group, has spent $7 million on similar messaging.

Democrat-aligned groups spent $17.2 million from the beginning of the race through Friday. Just over half of that was from outside groups, led by Majority Forward, a super PAC with close ties to Schumer.

The Democrat-aligned groups have attacked Collins, seeking to tie her to Trump, his aggressive immigration enforcement program and his efforts to slash spending on domestic programs.

Platner’s campaign has spent $5.9 million on ads, including spots responding to attack ads run by Mills and commercials attacking Collins.

And Mills, 78, has spent $1.8 million on ads highlighting her face-to-face confrontation with Trump and on spots highlighting Platner’s past internet comments about sexual assault.

Before April, the spending battle in the Senate race was somewhat tight. But Republican groups have opened up a huge advantage in prospective ad buys.

Between Friday and the June 9 primary, Republicans have booked $3.8 million in advertising, including $3.4 million by One Nation and nearly $400,000 from Collins.

Democrats have booked about $150,000 during that period.

Between the primary and Election Day, Republicans have booked $41.9 million in ads, compared to $20.3 million by Democratic groups.

The Republican total includes $28.8 million by the Senate Leadership Fund, a super PAC with close ties to Senate President John Thune, R-South Dakota. And Pine Tree Results, a pro-Collins super PAC, has booked another $12.6 million in ads.

Over that same period, all of the Democratic ad buys have come from WinSenate, a super PAC that in 2024 spent nearly $300 million opposing Republicans and $24.2 supporting Democrats, according to Open Secrets.