The full brief, which was filed with the U.S. Court of Appeals for the Sixth Circuit, is on SSRN:

This brief—filed by five law professors as amici curiae in United States v. Sittenfeld, No. 23-3840 (6th Cir.)—argues that the “clear and unambiguous” test supplies the appropriate standard for determining whether an alleged quid pro quo involving an otherwise-legal campaign contribution satisfies the explicitness requirement under McCormick v. United States, 500 U.S. 257 (1991).