Arkansas Rep. Marion Berry (D) on Sunday became the latest Democrat in a competitive House race to retire, sources said to the Washington Post's Chris Cillizza.

Berry is the sixth Democrat running in a competitive race to retire in the last couple months but is the first Democrat to retire since Scott Brown (R) won the Massachusetts special Senate election Tuesday.

"The message coming out of the Massachusetts special election is clear: No Democrat is safe," said National Republican Congressional Committee communications director Ken Span. "In the aftermath of Scott Brown's victory this past week, it has become evident to Democrats that to run for reelection in this toxic political environment is to ensure defeat at the ballot box in November."

Here is more from Cillizza:

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.