What is the burden of proving vindictiveness against a federal prosecutor who increases the severity of criminal charges following a procedural right?

1 If the government increases the severity of the charges following a defendant's exercise of a procedural right, the sequence of events gives rise to an appearance of vindictiveness, shifting the burden to the government to prove that the decision to re-indict with more severe charges did not result from any vindictive motive. "Instead, the prosecutor, to rebut the presumption, must show his decision to re-indict with more severe charges was 'justified by independent reasons or intervening circumstances which dispel the appearance of vindictiveness.' " United States v. Burt, 619 F.2d 831, 836 (9th Cir.1980), quoting United States v. Griffin, 617 F.2d at 1347.