Legal experts said Trump would have a stronger defense if he could show he did not know he was breaking the law. While ignorance of the law is not usually an excuse, campaign finance laws are treated differently, said Richard Hasen, a professor of election law at the University of California, Irvine. “For the campaign finance violation to be criminal, prosecutors would have to prove a wilful violation,” Hasen said. “If Trump did not know that he was violating campaign finance laws by directing the spending he would not be criminally liable.”