First, though, a little background. The Amendment, adopted in 1913, begins with great clarity: “The Senate of the United States shall be composed of two Senators from each State, elected by the people thereof, for six years...”

But its second clause is not so clear:

When vacancies happen in the representation of any State in the Senate, the executive authority of such State shall issue writs of election to fill such vacancies: Provided, That the legislature of any State may empower the executive thereof to make temporary appointments until the people fill the vacancies by election as the legislature may direct.

Back when civics class was a thing, most of us learned that the Constitution “gives” governors the power to name Senators to vacancies caused by death or resignation. But read the above carefully. In fact, the default rule is that an empty Senate seat, like an empty House seat, is to be filled by a special election. Under the “proviso,” however, a state legislature can decide to allow the governor to make “temporary appointments” until “the people fill the vacancies by election.”

This confusing language is there because the Amendment is what scholars call a palimpsest, a document that has been partially erased and reused, allowing traces of the old writing to bleed through. The original language of the Constitution required that senators be elected by the state legislatures; one clause actually did give the state “executive” the power to “make temporary Appointments until the next Meeting of the Legislature.” The drafters of the Seventeenth Amendment included a garbled version of this option.

The text leaves a puzzle: Can the legislature “empower” the governor just to fill a vacant seat for the rest of the term? How could that be a “temporary appointment”? What happens to the idea that the Senate is to be “elected by the people”? Where else in the Constitution do we give one person the power to appoint a constitutional official? I have done a good deal of research in the history of the Amendment, and cannot find an explanation of this provision anywhere.

I did that research while consulting with a group of Illinois lawyers who, five years ago, actually won a case under the Seventeenth Amendment. After Barack Obama resigned from the Senate, then-Illinois Governor Rod Blagojevich more or less openly conducted an auction to fill the rest of Obama’s term, ultimately naming Roland Burris. Illinois law allowed this, but we argued that an appointment for the entire term could not be “temporary,” and that the Seventeenth Amendment required a special election. Remarkably enough, the redoubtable Judge Diane Wood of the Seventh Circuit agreed with us, and the state was required to hold a special election—though the litigation took so long that it filled only the last 30 days of Obama’s term. It was a classic constitutional victory—rich in symbolism, a little hazy as to practice.