Resurgent Republicans captured control of the U.S. Senate Tuesday night in elections that are projected to complicate President Barack Obama’s final two years in office.

The Republican Senate leader, Mitch McConnell, held onto his seat in a hard-fought race with Democratic challenger Alison Lundergan Grimes in Kentucky. McConnell focused relentlessly on tying Grimes to President Barack Obama, who is unpopular in the state. McConnell now has the opportunity to become Senate majority leader.

Newcomer Republican Tom Cotton defeated two-term Democratic incumbent Mark Pryor of Arkansas, becoming the first domino to fall for the Democratic party. Democrats have held this seat for nearly 30 years. Tom Cotton will be the youngest senator at 37 years old.

Soon thereafter, Democratic Sen. Mark Udall lost a re-election bid in Colorado to Republican Cory Gardner.

Republican Shelley Moore Capito was the GOP winner for a Senate seat in West Virginia, a position that hasn’t been held by the Republican party since 1956. Capito is West Virginia’s first female senator to be elected.

Sen. Kay Hagan, a first-term Democrat, also lost in North Carolina to Republican Thom Tillis, the speaker of the state House.

Republicans also picked up open seats in South Dakota and Montana, where Democrats retired. They needed a net gain of six seats in all to end a Democratic majority in place since 2006.

Iowa provided the frosting on the cake as Republican Joni Ernst provided the seventh GOP pickup of the night, defeating Democrat Bruce Braley for the Senate seat held by retiring longtime Democratic Sen. Tom Harkin.

With races still undecided in such states as Alaska and Louisiana, Republicans held 52 seats to the Democrats 44.

Republicans also maintained their majority in the U.S. House of Representatives.