I would never take legal advice from anyone who identifies themselves as a "Trump ally":
According to a source, allies of Trump have told the president that [outgoing White House Chief of Staff John] Kelly could leak to reporters once he’s out of the White House, and are pushing Trump to get Kelly to sign an additional non-disclosure agreement. “People are worried that Kelly will be out there dropping bombs,” the source said.Any NDA they get Kelly to sign would not be enforceable under the First Amendment. Once he leaves, Kelly will be allowed to say whatever he wants, other than disclosing classified information. But he can't disclose classified information even if there is no NDA. The NDA makes no difference.