In Nevada, incumbent Sen. Dean Heller (R) staved off a challenge from Rep. Shelley Berkley, who tied herself to President Obama and relied on a turnout machine headed by Senate Majority Leader Harry M. Reid.

Nevada Sen. DeanHeller talks to the media after winning reelection to the Senate over challenger Rep. Shelley Berkley, D-Nev., Wednesday, Nov. 7, 2012, in Las Vegas. (Julie Jacobson -- Associated Press)

With nearly 98 percent of precincts reporting, the Associated Press declared Heller the winner. He captured about 45.9 percent of the vote, compared to 44.7 percent for Berkley.