It's an interesting question of law. All judges profess to uphold the separation of powers, but in reality the jurisprudence is "squishy" (<-- super technical legal jargon). Sure, the purse strings belong to the Legislative branch, but the Executive branch has plenary authority over international affairs. Could they take that angle, and would it work? Lots of room for judges to rule however they want. Me personally, I think you have to take a pragmatic view and call this an unlawful usurpation of power by the Executive. Would be nice to get some good precedent in the books.