Two assessments of the history of Supreme Court nominations in election years have hit the Interweb. The first is
A History of Supreme Court Nominations in Election Years, by
Paul Finkelman, on OUPblog. The second is an SSRN post by
Bryan H. Wildenthal, Thomas Jefferson School of Law,
Memorandum on Supreme Court Vacancies and Confirmations during Presidential Election Years. H/t:
Legal Scholarship Blog