Arkansas Lt. Gov. Bill Halter announced Monday that he will challenge Sen. Blanche Lincoln in the Democratic primary.

In a statement released Monday by his campaign, Halter, one of the most liberal politicians in the state, said he plans to file for the Senate race on Tuesday.

“Today I’m announcing that I will run in the Democratic primary for the United States Senate,” Halter said in a prerecorded video. “Washington is broken. It’s working for the special interests, not Arkansas families. … Enough is enough. It’s past time to put more Arkansas values in Washington.”

Halter’s entry into the race will be cheered by such groups as MoveOn.org, which had been openly pushing the lieutenant governor to take on the moderate Lincoln since last fall.

Lincoln has been focusing her campaign on appealing to conservative Democrats and independents who have grown concerned about her votes on health care and the economic stimulus package. In a primary with Halter, any move to the left could jeopardize her prospects in the general election.

At least half a dozen Republicans are vying for the opportunity to take on Lincoln in November. The leading GOP candidates are Rep. John Boozman and state Sen. Gilbert Baker.