In 2000, during the South Carolina primary election, purported pollsters (who were actually dirty tricks people working with the Bush campaign), called prospective voters and asked them if their vote would be affected if they discovered that John McCain had fathered a child with a black woman. (McCain and his wife adopted a Bengali girl, who was dark-skinned.) Obviously, the idea was to spread the rumor that the candidate had fathered an illegitimate black child. It is likely that McCain's defeat in SC that year was partially caused by that and other dirty tricks.
Now the same game, called "push polling", is being played with Barack Obama. In this case, the effort is to undermine him among Jewish voters in Florida by suggesting that he has links to the PLO and Hamas. (Thanks to Sara for pointing this out.)
Who do you think might be doing that?
US Jews report calls disparaging Obama - Israel News, Ynetnews