 if he's acting within statutory delegation and prerogatives given by Congress, he's presumed to have presidential immunity. It's a rebuttable presumption, though. You can prove that, well, no, they didn't really get to him. But if he's not doing it within statute or Constitution, and he's done something that's criminal or civil, let's say like had sex with an intern or something like that, you know, those types of things that might be a criminal offense –