PepsiCo said on Wednesday it is ending its endorsement relationship with the English soccer star David Beckham after 10 years.

As both presidential candidates prepare for the party conventions and publicly spar over economic issues and energy policy, they are also trying to win over big business.

Two economists contend that Oprah Winfrey’s endorsement of Barack Obama last year gave him a boost of about one million votes in the primaries and caucuses.

Where stars end and products and pitches begin has grown less and less discernible in the era of the human billboard.

The Teamsters union denied that its decision was in any way tied to the senator’s statement that federal supervision of the union had run its course.