Lawyerly readers will have noticed that the Court’s holding explicitly covers controversies between the executive and the judiciary while saying nothing about conflicts between the executive and Congress. Still it isn’t hard to see how the holding could be extended to the Senate in its most judicial role, exercising its “sole power to try all impeachments.” Just as jurors must evaluate all relevant testimony, goes the argument, so too must senators.

As Mr. Shaub points out, there are two kinds of executive-privilege claims. One is asserted to protect the general interest of the executive branch, current and future, in the confidentiality of internal communications, while the second cites the need to avert the harm that disclosure of specific communications might do to specific people or activities. U.S. v. Nixon applies explicitly to the former but not the latter.

Mr. Trump’s lawyers could try to argue that Mr. Bolton’s testimony would damage U.S.-Ukrainian relations or other important interests, delaying the conclusion of the Senate trial until the courts resolve the issue—if the judiciary is willing to review the matter. The courts might decline to do so, citing their longstanding reluctance to get involved in “political questions.” If so, the Senate subpoena would remain in force, and there is little doubt that Mr. Bolton would honor it, as he has said he would.