(CNN) - Add a primary challenge to Sen. Blanche Lincoln's growing list of political problems.
Arkansas Lt. Governor Bill Halter announced Monday morning that he's launching a Democratic primary challenge to Lincoln, who was already facing a tough re-election battle this year.
"Washington is broken. Bailing out Wall Street, with no strings attached while middle class Arkansas tax payers with the bill. Protecting insurance company profits instead of patients and lowering health costs. Gridlock, bickering and partisan games while unemployment is at a 25 year high. Enough is enough. It is past time to put more Arkansas values in Washington," said Halter in an anti-incumbent message in a video posted on his Web site.
Four progressive organizations, the Progressive Change Campaign Committee, Democracy for America, MoveOn.org, and Daily Kos, released an e-mail pledging to raise half a million dollars over the next week for Halter, who worked in President Bill Clinton's administration. Halter is expected to formally announce his primary bid Tuesday when he files papers of candidacy at the state capitol in Little Rock.
Halter's move means Lincoln will now add a challenge from the left to a number of challenges from the right. Since she teamed up with Vice President Joe Biden last year to launch her re-election bid for a third term, Lincoln has faced criticism from labor unions and progressive groups for what they describe as her move to right in order to save her seat.
Recent polls of Arkansas voters suggest Lincoln's approval rating and favorable ratings have dropped over the past year, a fact that's encouraged eight Republicans to battle for the GOP Senate nomination. A survey last month indicated that many of those Republican challengers were either leading or deadlocked with Lincoln in hypothetical general election matchups.
Update: White House Press Secretary Robert Gibbs confirmed Monday afternoon that President Barack Obama will support Lincoln in her primary fight with Halter.
–Follow Paul Steinhauser on Twitter: @psteinhausercnn