A Republican primary for a key Maine Senate seat is headed to ranked-choice runoff after no candidate received more than 50 percent of votes on Tuesday, with a sitting lawmaker best positioned to prevail. In Senate District 16, which includes Waterville, Winslow, Fairfield, Oakland and Albion, Rep. Mike Perkins, R-Oakland, led with 44 percent of votes, compared with 38 percent for Kevin Kitchin and 17 percent for Mark Andre. The race will go to a ranked-choice runoff between Perkins and Kitchin, with the second-choice votes from Andre supporters to be redistributed.