This does not mean that district courts do not confront questions of law in deciding whether to depart. In the present case, for example, the Government argues that the District Court relied on factors that may not be considered in any case. The Government is quite correct that whether a factor is a permissible basis for departure under any circumstances is a question of law, and the court of appeals need not defer to the district court's resolution of the point. Little turns, however, on whether we label review of this particular question abuse of discretion or de novo, for an abuse of discretion standard does not mean a mistake of law is beyond appellate correction. The District Court did not abuse its discretion in differentiating between the classes of cases, nor did it do so in concluding that unprovoked assaults constitute the relevant heartland.
Victim misconduct is an encouraged ground for departure.
A district court, without question, would have had discretion to conclude that victim misconduct could take an aggravated assault case outside the heartland. Congress did not grant federal courts authority to decide what sorts of sentencing considerations are inappropriate in every circumstance. The Guidelines, however, 'place essentially no limit on the number of potential factors that may warrant departure.' . . . The Commission set forth factors courts may not consider under any circumstances but made clear that with those exceptions, it 'does not intend to limit the kinds of factors, whether or not mentioned anywhere else in the guidelines, that could constitute grounds for departure in an unusual case.' . . . Thus, for the courts to conclude a factor must not be considered under any circumstances would be to transgress the policymaking authority vested in the Commission. . . .