President Trump's administration has just formally started the transition process. He is now officially a lame-duck President. It is common for outgoing Presidents to grant pardons in this last phase of their presidency, while they still have the power to do so; Clinton is one of the more infamous examples.
The question which occurred to me: Can a President shield people not only from punishment but even from investigation and trial for federal crimes by granting a pardon proactively (a "prospective pardon") before any prosecution, let alone indictment, trial, sentence or punishment?