Early election returns showed Coronado City Councilmember John Duncan leading in the race for mayor, with Mark Fleming and Laura Wilkinson Sinton leading for the two open positions on the council just after the polls closed Tuesday. A win by Duncan could bring a third vacancy to the City Council, since he’s only halfway through his four-year term. If elected, the city would need to determine how to fill his seat, whether through a special election or through council appointment. The other two men running for mayor, Mike Donovan and Casey Tanaka, are also currently serving on the council, but they both face term limits. Tanaka had the second-most votes Tuesday night, ahead of Donovan. In the election for two open seats on the City Council, Fleming and Sinton were leading in early returns, followed closely by Amy Steward. Three other candidates were farther behind: Mark Warner, Christine Mott and Andrew Gade. “I’m feeling great about the election; I left it all on the field,” Sinton said Tuesday evening. This year, both mayoral and city council races have been steeped in partisan politics that some candidates worried has overshadowed local issues. Although the races are technically nonpartisan, the San Diego County Democratic Party endorsed Sinton and Mott for council, while the local Republican party endorsed Duncan, Fleming and Warner. Outgoing Mayor Richard Bailey, who is termed out, also endorsed Duncan, Fleming and Warner. Coronado has historically had more registered Republican voters, but the city has seen a less pronounced conservative tilt in recent years, leading to more contentious races. As of the end of October, Coronado had 3,602 registered Democrats, 4,244 registered Republicans and 2,685 who did not state a party preference. Staff writer Alexandra Mendoza contributed to this report.