On election night, he had 44 percent of the vote compared to 55 percent for Gregerson. He failed to close that gap when more numbers were released Wednesday.
He now trails Gregerson, a 10-year veteran of the City Council, by 355 votes. More votes remain to be counted, but Marine said he saw Gregerson at City Hall and congratulated her on her likely victory.
"I would have to have a minor miracle at this point," he said.
If Gregerson goes on to win, it will buck a trend in local politics. It's not often that an incumbent mayor gets tossed. Marine, 51, has served two terms.
Gregerson is well-known in Mukilteo, though, having won five City Council races before this year. She also outspent Marine, roughly $18,000 to his $10,000.
While the spending gap doesn't sound huge on the surface, it represents a significant difference in a smaller city, said Todd Donovan, a professor of political science at Western Washington University.
"Door-to-door (visits), phone banking and direct mailing is all you've got," he said.
Marine's first six years as mayor were relatively free of controversy, but a couple of recent incidents at City Hall might have triggered his downfall.
In April 2012, the city's central computer system overheated and large chunks of data were lost. The information was later retrieved and Marine fired the city's IT director, but Gregerson and others accused Marine of lax oversight at City Hall.
In June this year, the city hired public works director Ron McGaughey, who had been accused of harassing female employees in a previous job in Okanagan County.
Marine said he was satisfied the allegations were untrue and stood behind the hire, but the situation further fueled criticism.
This was Marine's first serious test in his three mayoral elections. He ran unopposed when first elected in 2005 and was faced by a little-known challenger, Pat Smith, when re-elected in 2009.
He had two opponents in the August primary. In addition to Gregerson, he was challenged by City Councilman Steve Schmalz, an even more vocal critic of Marine.
In the primary, Marine had the most votes -- 1,730, compared to 1,389 for Gregerson and 1,158 for Schmalz.
Together, however, the two challengers out polled the mayor by roughly 800 votes, and it's likely most of the Schmalz voters swung to Gregerson.
Marine noted that the 1,425 votes he received in the general election so far are hundreds fewer than what he got in the primary. To date, 1,121 fewer votes have been tallied in the Mukilteo mayor's race compared to the primary.
"It's this low turnout that's killing me," he said.
In his campaign, Marine eschewed some of the more modern techniques used by Gregerson, including automated "robocalls" to voters' homes.
"We made some general calls (in person) reminding people to get out and vote. I'm not a big fan of robocalls," Marine said. "But I'm also not a big fan of negative campaigns. People say they don't like them, but it sways them."
Gregerson's campaign requested and received regular updates from the Snohomish County Auditor's Office election division about which voters had sent in their ballots and which ones had not. The information is available to any candidate or campaign for $11.50 per update, elections manager Garth Fell said.
Gregerson crossed off people who had already voted and focused mailings and calls on those who hadn't.
"We weren't mailing or calling anyone who had voted," she said.
Gregerson also had lists of likely voters and party registration. A database run by the state Democratic party made it easy to access that information, she said.
"We did that targeting through the whole race," Gregerson said. "We started in March. I spent my time with voters I knew were likely to be making the decision."
Marine said he believes some voters find robocalls irritating, but with the targeted lists, Donovan said, "you're not just calling everyone and annoying them, you're essentially reminding people to get out and vote. The way you get them to stop is to get your ballot in to the auditor."
In recent weeks Gregerson sent three mailings, which did not directly criticize Marine but pledged to halt tax increases. Marine sent one mailing.
Gregerson said it wasn't just having the data but "having volunteers three to five nights a week who are available to make those calls and reach out to people."
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