[Nursie]

Isn't he legally immune for anything done in the course of his duties?

You'd need pretty solid proof he was colluding with others to place trades, and not just running his tariff policies as he saw fit with advanced notice given to his inner circle as some sort of courtesy.

I'd be surprised if anything could be made to stick.

[actionfromafar]

Crucially, you need the proof, but you are not allowed to bring the proof to court!