Graphic: Shelly Tan, The Washington Post

A day after Republicans won back control of the West Virginia House of Delegates for the first time in eight decades, a Democratic state senator has changed party affiliation to give the GOP control of the state Senate as well.

State Sen. Daniel Hall switched his party affiliation this afternoon at the Secretary of State’s office in Charleston, the Charleston Daily Mail reported. The paper said a formal announcement is expected on Thursday.

Republicans were just a few seats away from a majority in the state House before Tuesday’s midterm elections, and party strategists were cautiously optimistic they could take enough seats to win back control of a traditionally Democratic state that has slipped toward the GOP in recent years. But the strength of Tuesday’s anti-Democratic wave gave Republicans a far greater number of seats than they had anticipated, and now Republicans stand to earn up to 64 of 100 seats in the House of Delegates.

Neither party anticipated a wave so strong it would put the state Senate in play. But when the votes came in Tuesday night, Republicans found themselves tied with Senate Democrats, 17 to 17.

Hall’s switch gives the GOP an 18 to 16 seat majority.

The Republican wave in West Virginia was part of an unexpected GOP sweep of state legislative chambers in the midterms. Republicans won control of seven other legislative chambers — the Senate and the Assembly in Nevada, the Colorado state Senate and House chambers in Minnesota, New Mexico, Maine and New Hampshire.

When new legislators are sworn in next year, Republicans will control 68 of 98 partisan legislative chambers around the country, six more than their previous high-water mark, which came after 2011 elections in Mississippi.

Republicans have total control — meaning  the legislature and the governor’s mansion — in 24 states, compared with just six states in which Democrats control all levers of the legislative process. The other 20 states are operating under divided control. Nebraska’s legislature, while technically is a unicameral nonpartisan body, is in practice run by Republicans.