That’s a good point, and I suppose that someone sympathetic to Trump might think that he was being unfairly prosecuted after other presidents hadn’t been.

I disagree with your implication that a former president should always be punished for having broken the law. The rules do need to be different for presidents than for ordinary people.

A prince, when by some urgent circumstance or some impetuous and unforeseen accident that very much concerns his state, compelled to forfeit his word and break his faith, or otherwise forced from his ordinary duty, ought to attribute this necessity to a lash of the divine rod: vice it is not, for he has given up his own reason to a more universal and more powerful reason; but certainly ’tis a misfortune: so that if any one should ask me what remedy? “None,” say I, “if he were really racked between these two extremes: ‘Let him see to it that it be not a loophole for perjury that he seeks.’ He must do it: but if he did it without regret, if it did not weigh on him to do it, ’tis a sign his conscience is in a sorry condition."

Montaigne’ Essays, book 3 chapter 1

It’s one thing to break a law with the belief (perhaps unjustified) that doing so is necessary for the good of the nation and quite another to do to because power protects you from deserved punishment, but how can the law itself make this distinction?