Arkansas Sen. Blanche Lincoln has failed to win the majority of votes in the Democratic primary. She now faces a three-week fight with Lt. Gov. Bill Halter for her party's nomination.

Already one of the most vulnerable incumbents seeking re-election this year, Lincoln is headed toward a June 8 runoff with Halter _ extending what's already been one of the most bitter and expensive political fights in Arkansas history.

Lincoln had said she would be ecstatic with either a runoff or a clear-cut victory in Tuesday's primary, but Halter has said that forcing her into a prolonged campaign would be close to a win for his bid.

Outside groups on both sides, including the AFL-CIO and the U.S. Chamber of Commerce, had pumped millions of dollars into the race.