According to WaPo and everyone:
Republicans won control of the Senate Tuesday evening as GOP candidates across the country swept to victory in crucial midterm elections, reflecting widespread unease about the nation’s direction and the electorate’s disenchantment with President Obama.
The GOP took control of Democratic held seats in Arkansas, Colorado, Iowa, Montana, North Carolina, South Dakota and West Virginia, giving the party seven additional senators. It had needed six to control the chamber for the first time since 2007.
The rapid-fire victories represented a repudiation of the president, who rode into office on a mantle of change in 2008 and was re-elected in 2012 but whose second term has bogged down in a problems ranging from crises abroad to the arrival of Ebola in the United States. Throughout the hard-fought the campaign, Obama was a target of Republican candidates and in the end was reduced to campaigning only in secure Democratic bastions.