Donald Trump Lashes Out at Jerry Seinfeld

Donald Trump is on the attack again and his new target is Jerry Seinfeld.

Trump is lashing out at Seinfeld for cancelling an appearance at a Trump-sponsored charity event.

Seinfeld bowed out because he feels "increasingly uncomfortable" with Trump's relentless questioning of President Obama's birthplace.

"He has respectfully withdrawn from the event," Seinfeld's agent confirmed today.

Trump's response was swift and brutal.

"You should be ashamed of yourself!" he wrote in a blistering letter. He even took aim at Seinfeld's short-lived show, The Marriage Ref on which he made a guest appearance.

"I agreed to do your failed show. I thought it was absolutely terrible and was embarrassed," said Trump.

The charity event, to raise money for St. Jude Children's Hospital, was organized by Trump's son, Eric, who appears on Celebrity Apprentice. It was to take place on September 13th at the Trump National Golf Club in Briarcliff Manor.

This latest Trump feud comes as a new CBS/New York Times poll of Republican voters puts him a disappointing fifth among potential GOP candidates. Mike Huckabee tops the list.

And 72% of Republican voters actually say he's not a serious candidate.

Seinfeld says he will still be making contributions both to Eric Trump's foundation and St. Judes.