Tennessee Sen. Bob Corker has fended off four challengers in a Republican primary to win his party's nomination for a second term.

The former Chattanooga mayor faced a much easier time in his re-election bid than he did when he ran in 2006. Then he had a tough primary against two former congressmen and narrowly defeated former Democratic U.S. Rep. Harold Ford Jr. in an even-more bruising general election campaign.

Democrats nominated floor installer Mark Clayton from among seven largely unknown candidates vying for the nomination to face Corker in the general election.

In the most recent financial disclosures, Corker had more than $6 million remaining, while no other challenger had more than $19,000.

In other closely watched races, freshman U.S. Reps. Diane Black and Chuck Fleischmann turned back vigorous attempts by Republican rivals to deny them another term in Congress.