Arkansas Rep. Marion Berry is expected to announce his retirement tomorrow morning, according to three sources briefed on the decision.

Berry will become the sixth Democrat in a competitive seat to leave in the last two months but the first to announce his retirement since the party's special election loss in Massachusetts last Tuesday.

"The message coming out of the Massachusetts special election is clear: No Democrat is safe," said National Republican Congressional Committee communications director Ken Spain.

Berry, first elected in 1996, had been noncommittal about his re-election bid for months although, privately, his allies insisted he was planning to run for re-election.

While Berry had rarely been challenged in the 1st district over the past decade or so, the seat has a clear Republican tilt as Arizona Sen. John McCain (R) won it with 59 percent in 2008.

Arkansas will be a huge focus of Republican efforts in the fall with Berry and Rep. Vic Snyder (D) retiring and Sen. Blanche Lincoln (D) in deep trouble as she seek re-election.

The field to replace Berry isn't yet set although Democrats mentioned include state Rep. Keith Ingram, Berry chief of staff Chad Causey and Jason Willett, a former state party chair. State Attorney General Dustin McDaniel (D) is regarded as a rising star in the state and would be a favorite if he ran. On the Republican side, broadcaster Rick Crawford is in the race although the field is likely to expand with the Berry announcement.

Berry joins Snyder as well as Reps. Dennis Moore (Kans.), John Tanner (Tenn.), Brian Baird (Wash.) and Bart Gordon (Tenn.) as Members sitting in districts either won by McCain or carried narrowly by President Obama to step aside between the end of November and today.

Democratic strategists warned privately that a Coakley loss could open the floodgates for members who were wavering about their future political plans. Including Berry, there are now 12 Democratic members retiring with 14 Republicans calling it quits.

The next two weeks could well serve as a tipping point in the battle for House control. Today there appear to be too few open Democratic seats for Republican to win the 40 seats they need to take control. But, another handful of retirements in swing districts could imperil Democrats hold on the chamber.

By Chris Cillizza  |  January 24, 2010; 7:25 PM ET