Legal Question in Constitutional Law in Florida

The scenario you describe is very unlikely, even assuming that there are grounds to charge Ms. Clinton. Whether to bring federal charges is up to the U.S. Attorney in the district where the crime allegedly occurred. Each U.S. Attorney has a great deal of independence. If they believe a case is worth pursuing, they pursue it. If a President ever ordered a U.S. Attorney not to bring charges that she believed should be brought, she would almost certainly resign and go public with her reasons.

Assuming that your scenario really comes to pass, Ms. Clinton could still be charged later. A decision not to prosecute isn't final until the statute of limitations has run. So if there is still time left when the next administration takes office, it would be able to file the charges.

One thing President Obama *could* do would be to pardon Ms. Clinton before he leaves office. That would protect her from federal charges for whatever actions the pardon covers. That seems very unlikely to happen, regardless of how strong or weak any case against Mrs. Clinton might seem at the time.

One more point: Suspects are sometimes granted immunity, either to get their testimony (witnesses can only invoke their Fifth Amendment right not to testify if prosecutors can use the testimony against them, which can't happen if the witness is immune) or as part of a deal to cooperate in prosecuting someone else. Witnesses only get immunity when prosecuting the other person is a higher priority, which would not happen here.