Prosecuting attorneys have such influence and control over grand juries that they can get them to indict a ham sandwich. And federal criminal law is so broad in scope that all ham sandwiches are potential legal targets.
Because of his pardon power, the President has a weapon to defend himself from being ham sandwiched. The hatred of his enemies is so intense, and their position within the Deep State so strong, that he will need to exercise the pardon power to disarm them.
It’s a matter of timing. Trump has an intuitive understanding of political timing, and is waiting for the right moment. The sooner the better.
They got Nixon, but Nixon was guilty. Trump is innocent. He will prevail if he uses his constitutional powers to defend himself..