Whatever one calls it here, it simply isn’t an evidence question: It’s not about whether to admit into evidence a particular document, but about obtaining that document in the first place; and it’s not about whether a witness must answer a specific question, but about forcing that witness at least to show up. And that threshold question falls squarely under Rule V — meaning under the chief justice’s authority alone. And that’s why the Senate, despite outlining the rules for subpoenas, never made its subpoena rules governed by Rule VII.

If there were any doubt, recall the language of the Constitution, which orders that, in an impeachment trial of the president, “the Chief Justice shall preside.” To “preside” is not a merely symbolic role; it can mean, just as it meant during President Andrew Johnson’s impeachment trial, to be asked to make a range of actual rulings, including ones on which the chief justice is not merely the first word but also the last.

There’s a reason that, to our knowledge, no chief justice presiding over a president’s impeachment trial has had to confront precisely this issue before: No president has tried to hide all of the facts from Congress before. To be sure, previous presidents facing the prospect of impeachment — like Presidents Nixon and Clinton — have been accused of failing to share all of the information sought from them. But none ever vowed, as Mr. Trump has, to continue “fighting all the subpoenas” regardless of their particular validity. Ultimately, some accommodation was reached in previous impeachment inquiries as to the scope of information provided — including, for Mr. Clinton’s impeachment trial, an eventual agreement on witness testimony. If Chief Justice Roberts is being asked to answer difficult questions, it is a direct result of President Trump’s scorched-earth approach to congressional oversight.

The framers’ wisdom in giving this responsibility to a member of the judiciary expected to be apolitical and impartial has never been clearer. With key Republican senators having told the American people that they prejudged the case against President Trump before it began and even working with Mr. Trump’s lawyers to build the very defense for which they’re supposed to be the audience, the notion that they’re doing the “impartial justice” they’ve sworn to do is very much in question.

The Democrats’ impeachment managers should immediately ask the chief justice to issue subpoenas for key witnesses and documents, insisting that the Senate rules make him and him alone the decision maker about whether to “make and enforce” those subpoenas. That’s his prerogative — and his responsibility, one he can’t simply shift to the senators as permitted for evidentiary questions under the Rule VII carve-out.

What happens next won’t be totally within Democrats’ or the chief justice’s control. As Representative Adam Schiff acknowledged Thursday, the chief justice can decide evidence questions like executive privilege, but his determinations can be overruled by a majority of senators.