within the scope of his presidency when he said what he said, not that it was OK to say it. If he was acting in that capacity the government is obligated to raise a defense on his behalf and substitute itself as the defendant. The catch, of course, is that the government can't be sued for defamation, so the government would be off the hook for damages. in Clinton v. Jones, the Supreme Court case held that a sitting president of the United States is not immune from litigation for acts done before taking office and unrelated to the office, but this is a case involving an act done while the president was in office. So they have to rely on Nixon v. Fitzgerald, which held that a president is absolutely immune from litigation for discretionary acts done while in office. The decision is very broad, and although it doesn't define exactly which activities Fitzgerald covers, the case is generally interpreted to mean that as long the action is within the broadest understanding of the president's function as president, he's immune. The reason the appeal is being taken by the current DoJ is not to protect Trump but to determine, by an appellate court, where that line is. The notion that a president can make allegedly libelous statements regarding a situation not related to his function as president is a huge stretch and it will probably fail, as it should. But it is in no regard inappropriate for the DoJ to want to get an answer to the question for the sake of future administrations.