HELENA, Mont. (AP) -- U.S. Sen. Jon Tester has won a second term, fending off a challenge from Republican U.S. Rep. Denny Rehberg.

Tester and Rehberg had been in a close contest for nearly two years as each struggled to break the race open despite a dizzying number of attack ads.

Tester ran a campaign touting his work to help Montana. Throughout, he attacked Rehberg as a career politician who had few results to show for it.

Tester survived Rehberg's relentless attacks tying him to unpopular Obama administration policies. Rehberg is a six-term congressman who will leave office at year's end.

The Senate now stands at 52 Democrats, 45 Republicans and two independents. The Senate race in North Dakota remains too close to call.