I view this concurrence as something of a compromise. On the one hand, Gorsuch and Kavanaugh generally favor a broad conception of executive power. The two junior members of the Court were not prepared to join the chief’s opinion, which handcuffs the president’s autonomy and alters the balance of authority between the federal and state governments.
On the other hand, in this case too, Gorsuch and Kavanaugh likely could not be seen as voting in favor of the president who appointed them — especially after their contentious confirmations. They needed to stand in the same shoes as the Nixon appointees who ruled against President Nixon four decades ago. Indeed, during his confirmation hearing, Kavanaugh praised Chief Justice Warren Burger, “who had been appointed by President Nixon” and “brought the Court together in a unanimous decision.” At the time, Kavanaugh knew that he could be called on to decide the validity of a subpoena against President Trump — whether it came from Robert Mueller, the House of Representatives, or a state prosecutor. There were no surprises.
Kavanaugh and, I suspect, Gorsuch understood this dynamic all too well. These judges were very much attuned to how they would be judged. So they split the difference. In voting for a framework that empowered future presidents to resist subpoenas, they also cast a hyper-technical vote that allowed New York’s subpoena to be enforced against the current president. To the general public, the vote was 7–2. It was not unanimous, but this lopsided split was better than 5–4. And to Kavanaugh and Gorsuch, their short writing did not disturb the long-term constitutional equilibrium.