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Old Town Today
By the People, for the People
Third Democrat Enters Maine Senate Race
David Costello joins Janet Mills and Graham Platner in challenging Republican incumbent Susan Collins
Mar. 16, 2026 at 8:49pm
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David Costello, an Old Town native and former government official in Maine and Maryland, has officially entered the race for the Democratic nomination to challenge incumbent Republican U.S. Senator Susan Collins in Maine's high-profile 2026 midterm election. Costello, who previously ran against independent Senator Angus King in 2024, will face off against fellow Democrats Janet Mills and Graham Platner in the June 9 primary.
Why it matters
The race for Maine's U.S. Senate seat is expected to be one of the most closely watched and competitive in the country, as Republicans look to defend their narrow majority in the upper chamber. Costello's entry into the race adds another experienced Democratic challenger to the mix, potentially making the primary contest more heated and the general election battle more intense.
The details
Costello, an Old Town native, qualified for the June 9 Democratic primary by gathering the required number of voter signatures. He previously ran against independent Senator Angus King in 2024, though he was unsuccessful in that bid. Costello has held government roles in both Maine and Maryland, giving him experience in public service that he hopes will resonate with voters.
- Costello officially entered the race on March 16, 2026.
- The Democratic primary election in Maine is scheduled for June 9, 2026.
The players
David Costello
An Old Town native and former government official in Maine and Maryland, Costello is the third Democrat to enter the race to challenge incumbent Republican U.S. Senator Susan Collins.
Janet Mills
The former governor of Maine, Mills is one of the other Democrats vying for the party's nomination to take on Senator Collins.
Graham Platner
Platner is the third Democrat running in the primary to determine who will face off against Senator Collins in the general election.
Susan Collins
The incumbent Republican U.S. Senator from Maine, Collins is seeking re-election in 2026.
Angus King
The independent U.S. Senator from Maine, King was previously challenged by Costello in the 2024 election.
What they’re saying
“I'm running for Senate because Mainers deserve a fighter who will put their needs first, not the special interests. As a former state and federal official, I have the experience to get results for Maine families.”
— David Costello
What’s next
The Democratic primary election in Maine is scheduled for June 9, 2026, where Costello will face off against fellow Democrats Janet Mills and Graham Platner. The winner of that primary will then challenge incumbent Republican Senator Susan Collins in the November general election.
The takeaway
The entry of David Costello into the race for Maine's U.S. Senate seat adds another experienced Democratic challenger to the mix, setting up what is expected to be a highly competitive and closely watched primary and general election battle for this crucial Senate seat.
