Impeachment can be based on  non-criminal misconduct 
  Kentucky Law Journal (2025) (forthcoming)
  
Clark D. Cunningham & Ute Römer-Barron
Appendix
  http://www.clarkcunningham.org/Impeachment-Appendix.html
"high misdemeanor" has largely disappeared from American vocabulary
  
"high misdemeanor" in Founding Era texts
-Search results from Founders Online (annotated)
-Search results from Corpus of Founding Era American English (COFEA) (annotated)
Madison papers: usage of "other noun + noun"
Madison papers: usage of "high noun + noun"
Corpus evidence that "crime" and "misdemeanor" were not used as synonyms
  - Corpus of Founding Era Amercan English (COFEA)
  -- Search results for "crim* or misdem*" (63 examples)
  -- Search results for "misdem* or crim*" (1 example) 
-Founders Online 
-- Search results for "crim* or misdem*" (23 examples)
-- Collocate comparison between "crime" and "misdemeanor" 
Records of the Federal Convention of 1787
  -- July 20, 1787 
  -- August 28, 1787 (image) (text) 
  -- September 8, 1787 
Articles of Impeachment
  -- Judge John Pickering (1804)
  -- Judge James Peck (1830)
  -- President Andrew Johnson (1868)
  -- William Belknap (1876)
  -- Judge Charles Swayne (1905) 
  -- Judge Robert Archbald (1912)
  -- Judge George English (1926) 
  -- Judge Halsted Ritter (1936)
Randolph's 1681 Articles of high Misdemeanor
Accusation of High Misdemeanor against President Thomas Jefferson (1809)
An Act to define and punish certain Conspiracies (July 31, 1861)