Mayor Michael Bloomberg urged Jewish voters to denounce the whisper campaign that for months has pushed the false rumor that Democratic presidential candidate Barack Obama is secretly a Muslim. Bloomberg warned a Jewish group in Boca Raton, Florida, on Friday that the attempt to portray Obama as a shadowy Muslim with a hidden agenda often targets Jewish voters online and with e-mails. The deceptive campaign against Obama, who is Christian, "threatens to undo the enormous strides that Jews and Muslims have made together in this country," the New York mayor said. The lies are "cloaked in concern for Israel, but the real concern is about partisan politics," said Bloomberg, who is Jewish. "This is wedge politics at its worst, and we've got to reject it - loudly, clearly and unequivocally." Bloomberg, a billionaire independent, had considered making his own run for the White House this year, but decided against it. He has said his endorsement and potential financial backing could still be up for grabs, and there has been occasional chatter about how he might make a good running mate for either Obama or Republican John McCain. Either way, Bloomberg's passionate defense of Obama in front of a Jewish audience in Florida could help the Illinois senator in the state, which is home to many Jewish voters. Some have questioned Obama's commitment to Israel; this stems partly from his stated willingness to talk with leaders of rogue nations, which McCain and others have criticized as a sign he underestimates the threat posed to Israel by Iran and others in the Middle East. There is also uneasiness about Obama among some Jewish people because his former church pastor has praised black Muslim leader Louis Farrakhan, who has made anti-Semitic remarks. Obama has disavowed his pastor and left the church. Earlier this month in a speech to Jewish activists in Washington, Obama referred to the e-mail campaign against him as one "filled with tall tales and dire warnings." Bloomberg noted how racial and religious tensions have cooled, and remained calm, in New York City - an achievement for which he is often praised. One thing he has learned, Bloomberg said, is that one must speak out against those who spread "fear and stereotypes." "That's why I'm speaking out today," he said, "and I hope all of you will join me throughout this campaign in strongly speaking out against this fear mongering, no matter who you'll be voting for."