Robert G. Natelson (Independence & Montana Policy Institutes) has posted Impeachment: The Constitution's Fiduciary Meaning of 'High . . . Misdemeanors' (19 Federalist Soc'y Rev. 68 (2018)) on SSRN. Here is the abstract:
This essay explores the meaning of the phrase “high ... Misdemeanors” in the Constitution's Impeachment Clause. After a review of 18th century sources, it concludes that the phrase denotes breaches of fiduciary duties.