Comment by TheCoelacanth

The first amendment still applies because defamation wouldn't be illegal without the US government passing a law to make it illegal. That means that the US's defamation laws can only restrict speech within the very narrow exceptions to the first amendment that courts have allowed.

The bar is especially high for defamation of public figures like Nixon. For something to be defamation against a public figure, it not only has to be provably false; it has to be intentionally and maliciously false. They would have to prove that the author intentionally was spreading false information to hurt the subject. That is so difficult to do that defamation suits regarding public figures are almost never successful.