suing for defamation in the US

""I'm also challenging the young woman and the lawyers to level those charges against me outside of the courtroom, so that I can sue them for defamation".  This is what I want to know: how can Dershowitz who appears almost daily on TV be able to sue for defamation in US courts when I was told by several lawyers in the US that I can't sue for defamation in US courts because I am considered a "public figure", due to this blog and to public appearances? Or do the laws on defamation apply differently in cases of Zionist hoodlums?