Election officials say a ranked-choice voting tabulation aimed at determining the winner of a key congressional race in Maine starts in the coming week.

Republican leaders are projecting confidence that they will keep control of the U.S. House as more races were decided in their favor Thursday, while Democrats insist they still see a path toward the majority and sought assurances every vote will be counted.

The race to represent Maine’s Second Congressional District, one of the most closely-watched in the nation that could help determine control of the US House of Representatives, is headed for a runoff, despite the objection of the incumbent, officials said.