The party protected vulnerable incumbents and picked off Democrats in competitive districts, handing the president-elect a unified Congress to enact his agenda.

More than a week after Election Day, control of the House of Representatives has yet to be decided. Out of the 435 seats in Congress’s lower chamber, 12 have yet to be called. How many of these seats — most of them concentrated in slower-counting Western states such as California and Arizona — does each party need for a 218-seat majority?