"Amarica's Constitution" welcomes our guest, Professor Michael Gerhardt, who pulls himself away from his work as Congress' go-to expert on the impeachment to share a postmortem with us from the inside.   He should know - he was retained by the presiding officer, Senator Leahy, as counsel for the impeachment.  His new book, "Lincoln's Mentors," is out, and we can't ever resist a Lincoln discussion.  Andy and Akhil  have been teasing about EverScholar - today they let us know what all the fuss is about; see for yourself at everscholar.org.