If this film is the dreck that the Whitehouse and mainstream news says it is, why isn't Gilbert being sued for slander? Do they not have the money, or is it that they are afraid of what will actually be solidified in evidence. Tom Cruise sued over gay claims, this is claiming Obama is the bastard son of a communist and a libertine amateur porn star mother!
shareTo successfully sue for slander you would have to prove the defendant was knowingly lying. Since the disclaimer at the beginning of the film probably puts this in the category of the director's "opinion" rather than him claiming to state facts, successfully suing himself would probably be tough.
That and false claims against leading politicians are so common that I doubt any of them find detractors like this worth their time and effort.