With almost all precincts reporting, Mr. Obama won 75 percent of the vote in the District of Columbia and 64 percent in Virginia. He had 60 percent of the vote in Maryland with results from 67 percent of the precincts.

On the Republican side, Senator John McCain won in Virginia over Mike Huckabee, the former governor of Arkansas, virtually eliminating any threat that Mr. Huckabee might have posed to Mr. McCain’s status as his party’s all but certain nominee.

Mr. Huckabee got a boost from conservative and evangelical Christian voters in the state, but not enough to overcome support among moderates and nonevangelical Christians for Mr. McCain, who won 50 percent of the vote. Mr. McCain also prevailed in the District of Columbia, with 68 percent of the vote, and in Maryland, where he had 55 percent of the vote with 67 percent of the precincts reporting.