The point is not that the Court got Vance wrong. To the contrary, the majority’s reasoning is convincing, and none of the specific arguments that President Trump’s lawyers advanced for why complying with subpoenas would interfere with his official duties holds water. Rather, the point is that Vance raised genuine, weighty constitutional concerns derived from the structure of the federal union. It’s not at all implausible or unreasonable to find a state-government-issued subpoena to a sitting president uniquely troubling, or to think that such subpoenas should be subject to a special rule. The issue in Vance is complex and difficult, exactly the kind of dispute that needs to be resolved by the Supreme Court, and that is just what the Court did.
Mazars, by contrast, should have been an easy win for Congress. But that’s not what happened. Rather, the Court held that a special rule does limit Congress’s ability to investigate the president. But where does this rule come from? Chief Justice John Roberts simply asserts that congressional subpoenas for presidential records raise “significant separation of powers concerns.” He seems to mean nothing more by this than that they involve a confrontation between Congress and the White House, which he would clearly rather not have his Court be dragged into. Hence the opening recitation of a lengthy history, this time dating back to 1792 in the Washington administration, to show that similar disputes have usually been settled through interbranch negotiation and compromise. This history informs Roberts’s refusal to accept that Congress has an essentially unlimited power to investigate the president, which, he notes, would mean that Congress could short-circuit the traditional negotiation process and simply win every time.