Obama got a boost from newly released results from Saturday's Washington state caucus, and he extended it with wins Tuesday in Virginia, Maryland and the District of Columbia.
Obama won at least 51 delegates in Tuesday's primaries, with 93 still to be awarded. Clinton won at least 24.
Obama won 53 of Washington state's 78 delegates, according to an Associated Press analysis of caucus results released by the state party Tuesday night. Clinton won 25.
In the overall race for the nomination, Obama had 1,210, including separately chosen party and elected officials known as superdelegates. Clinton had 1,188.
It will take 2,025 delegates to secure the Democratic nomination.
Sen. John McCain picked up all 60 delegates from winning the Virginia primary. A total of 113 Republican delegates were at stake in primaries in Virginia, Maryland and the District of Columbia.
Overall, McCain had 789 delegates and former Arkansas Gov. Mike Huckabee has 241.
It will take 1,191 delegates to secure the Republican nomination.
The AP tracks the delegate races by projecting the number of national convention delegates won by candidates in each presidential primary or caucus, based on state and national party rules, and by interviewing unpledged delegates to obtain their preferences.
In some states, like Iowa and Nevada, local precinct caucuses are the first stage in the allocation process. The AP uses preferences expressed in those caucuses to project the number of national convention delegates each candidate will have when they are chosen at county, congressional district or state conventions.
