Obama's campaign

Democratic presidential hopeful, Sen. Barack Obama, speaks to people at Waterfront Park in Portland, Oregon on Sunday, May 18, 2008. (AP Photo/Chris Carlson)

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Democratic presidential hopeful, Sen. Barack Obama, speaks to people at Waterfront Park in Portland, Oregon on Sunday, May 18, 2008. (AP Photo/Chris Carlson)

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Democratic presidential hopeful Barack Obama, smiles as he jokes with the crowd during a campaign appearance in Pendleton, Oregon on Sunday, May 18, 2008. (AP Photo/Don Ryan)

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Democratic presidential hopeful US Senator Barack Obama (L) watches as former US Senator and presidential hopeful John Edwards greets supporters during a rally at Van Andel Arena, Michigan on May 14, 2008. (Photo/Mark Wilson)

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Democratic presidential hopeful US Senator Barack Obama (R) greets former US Senator and presidential hopeful John Edwards (L) during a rally at Van Andel Arena, Michigan on May 14, 2008. (Photo/Mark Wilson)

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