Pardon them for what? You have to commit a crime to be pardoned and nobody has even been charged of anything yet. If Trump tried that he'd be right back to obstruction of justice again and impeachment would be a foregone conclusion.
And let's try to remember. Trump only cares about his own neck. When his cohorts are looking at time, they'll be singing like canaries to save themselves. Why do you think Flynn asked for immunity? He was going to sing. Why do you think Scooter Libby went to jail? A President can only issue pardons after the fact and only then if he escapes impeachment by the Senate.
So no. There is no power of the Constitution that Trump can use and for very good reason. We aren't living under a dictatorship quite yet.