Obama's campaign plans a 1 p.m. conference call Wednesday to announce the endorsement by David Wilhelm, who later became chairman of the Democratic National Committee. The aide spoke on condition of anonymity because the announcement would be made public later in the day.

Wilhelm plans to tell reporters that Obama can build a coalition of Democrats, independents and Republicans needed to win the general election. He also says Obama can bring the change he promises—improving the economy and ending the war in Iraq.

Wilhelm is a superdelegate from Illinois who was previously uncommitted in the race.

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