Libel still can be successfully prosecuted in America if “actual malice” can be shown and the account is untrue. It is not impossible.
Private figures can win a libel lawsuit much more easily due to relatively minor mistakes without actual malice.
The bar is very high but not impossible to meet with public officials and public figures — proving “reckless disregard for the truth” is commonly the focus of the libel lawsuit if it's clear that there was a serious error of fact.
But what appears to have happened with “Free Dominion” could not have happened under current American libel law. The person who brought the lawsuit is unquestionably a public figure, with all the high standards of proof that requires.
I'm anything but a fan of the ACLU, but on this issue of “hate speech,” the liberals are divided and there's a significant group of American liberals who are quite emphatic on the older ACLU position of allowing such things as the Nazi march in Skokie. I personally think Nazis should be prosecuted as traitors, but that's a whole different issue.