Oh, heck. At first I thought you found the silver bullet. Indict Hillary for treason. But I looked it up and I think you're wrong. From Wikipedia:
In the United States, the pardon power for federal crimes is granted to the President of the United States under Article II, Section 2 of the United States Constitution which states that the President "shall have power to grant reprieves and pardons for offenses against the United States, except in cases of impeachment".
Oops, sorry, you’re right. I remembered that there was a single exception, but misremembered want that exception was.