Patrick Murray (Dayna Smith/For The Washington Post)

“This decision to run for a second time took much soul-searching, thought and prayer,” Murray said in an e-mail to supporters that was published by “Campaigns are a crucible, but, just as with my military service, this is a matter of duty for me.”

Moran defeated Murray in the last cycle, 61 percent to 37 percent, even though Republicans did extremely well in other races across Virginia and the country. Murray’s task will likely be even tougher in 2012, with President Obama atop the ballot to drive turnout. (Obama got 69 percent of the vote in the 8th district in 2008.)

The 8th currently includes Arlington, Alexandria, Falls Church and part of Fairfax County. The redistricting process, which will now take place in early January, will likely remove from the district some portions of western Fairfax along the Dulles Toll Road, and add some territory to the south, around Lorton.

Murray’s decision was not a surprise; he said back in February that he was “leaning toward” making another run at Moran, and he has lobbed a steady stream of criticism at the Democrat all year.