Susan Davis

USA TODAY

WASHINGTON — Republicans took control of the U.S. Senate in a series of stinging defeats for Democrats and President Obama, who will face a unified GOP-controlled Congress for his final two years in office.

Senate Minority Leader Mitch McConnell, R-Ky., will become majority leader in January after he glided to re-election Tuesday against Democratic Secretary of State Alison Lundergan Grimes.

Obama asked congressional leaders to meet with him at the White House on Friday.

"We do have an obligation to work together on issues where we agree," McConnell said Tuesday evening in his victory speech. "Just because we have a two-party system doesn't mean we have to be in perpetual conflict."

Republicans enjoyed five takeovers early Tuesday evening of Democratic-held seats in Arkansas, Colorado, Montana, West Virginia and South Dakota.

North Carolina Republican Thom Tillis provided the sixth GOP takeover to tip the Senate in the GOP's favor when he narrowly defeated Democratic incumbent Sen. Kay Hagan. Republicans picked up a seventh seat in Iowa after Republican Joni Ernst defeated Democratic Rep. Bruce Braley in an open seat race to replace retiring Democratic Sen. Tom Harkin.

Democrats held no further prospects for takeovers of their own, leaving the GOP a guaranteed takeover even as the Democratic-held seats in Alaska remained undecided and Louisiana was headed to a runoff.

Incumbent Democratic Sen. Mark Pryor of Arkansas was ousted by GOP Rep. Tom Cotton, and Colorado Sen. Mark Udall was ousted by GOP Rep. Cory Gardner. GOP Rep. Shelley Moore Capito made history as the first woman elected to serve West Virginia in the Senate. Former South Dakota governor Mike Rounds cruised to victory for an open seat despite late Democratic attempts to make the seat competitive.

GOP Rep. Steve Daines faced only token opposition in Montana, which slipped away from Democrats months ago after incumbent Sen. John Walsh dropped out of the race following revelations that he plagiarized his master's thesis at the Army War College. His degree was revoked in October.

As Obama's approval ratings hovered in the low 40s and the battle for control largely played out in states Mitt Romney won in 2012, Senate Republicans enjoyed sweeping victories. The GOP further fended off a challenge from Democrat Michelle Nunn, the daughter of a popular former Democratic senator, when businessman David Perdue surpassed the 50% threshold to avoid a runoff Jan. 6, keeping the seat in GOP hands.

Overall, 36 Senate seats were up for re-election Tuesday, but 11 Republican incumbents and 10 Democratic incumbents were sailing to re-election in non-competitive races.

Battle for control of the Senate had focused in 10 states. Democrats controlled the Senate 55-45, with the help of two independents. Republicans needed a net gain of six seats to take control of the chamber because Vice President Biden would have been the tiebreaker in a 50-50 Senate.

The Senate will see new faces in Oklahoma and Nebraska. Oklahoma GOP Rep. James Lankford easily won the race to fill out the term of Sen. Tom Coburn, who is retiring early, and Ben Sasse won the Nebraska seat held by retiring GOP Sen. Mike Johanns.

Republican Sens. Tim Scott and Lindsey Graham of South Carolina, Susan Collins of Maine, Jeff Sessions of Alabama, Thad Cochran of Mississippi and James Inhofe of Oklahoma all sailed to re-election. Among Democrats, Sens. Cory Booker of New Jersey, Chris Coons of Delaware, Ed Markey of Massachusetts and Majority Whip Dick Durbin of Illinois — soon to be in the minority — were easily declared winners.

Heading late into election night, incumbent Democratic Sen. Mark Begich was in a precarious polling position despite hailing from a well-known political family. Obama's unpopularity in Alaska was a drag on Begich's campaign, and Republican Dan Sullivan was well-positioned to pad the GOP's new majority to 53 seats.

One bright spot for Democrats was New Hampshire, where Sen. Jeanne Shaheen defeated former Massachusetts GOP senator Scott Brown, who lost in 2012 and later moved to the Granite State to run for the Senate again.

Virginia Democratic Sen. Mark Warner was locked late Tuesday in a surprisingly narrow race against Republican Ed Gillespie, a former national Republican Party chairman.

One wild card in Tuesday's races had been Kansas independent Greg Orman, who challenged GOP Sen. Pat Roberts, but Orman was defeated, taking with him the prospect of caucusing with Democrats.

A race in Louisiana headed to a runoff Dec. 6 because neither incumbent Sen. Mary Landrieu nor her GOP challenger, Rep. Bill Cassidy, crossed the 50% threshold required to declare victory.

Louisiana will be a challenge for Democrats to hold as their voters are less likely to turn out than Republican voters in a midterm election year, and the GOP is confident it will win the state. If Louisiana and Alaska fall to GOP, Republicans will start the new Congress with a 54-seat majority.

In a statement, Senate Majority Leader Harry Reid, D-Nev., congratulated McConnell and said he stands ready to work with him.

"The message from voters is clear: they want us to work together," Reid said.