In United States v. Armstrong, the Supreme Court explicitly set forth the threshold requirement the defendant must meet in order to be entitled to discovery on a selective prosecution claim. There must be a credible showing that similarly situated persons of other races could have been prosecuted, but were not.
Brand, Robert C.
"United States v. Armstrong: Permissible Prosecutorial Discretion?,"
Mercer Law Review: Vol. 48
, Article 13.
Available at: https://digitalcommons.law.mercer.edu/jour_mlr/vol48/iss3/13