A Legal Outsider, an Offbeat Theory and the Fate of the 2024 Election

In the world of American legal scholarship, Seth Barrett Tillman is an outsider in more ways than one. An associate professor at a university in Ireland, he has put forward unusual interpretations of the meaning of the U.S. Constitution that for years have largely gone ignored — if not outright dismissed as crackpot.

But at 60, Professor Tillman is enjoying some level of vindication. When the U.S. Supreme Court considers on Thursday whether former President Donald J. Trump is barred from Colorado’s primary ballot, a seemingly counterintuitive theory that Professor Tillman has championed for more than 15 years will take center stage and could shape the presidential election.

The Constitution uses various terms to refer to government officers or offices. The conventional view is that they all share the same meaning. But by his account, each is distinct — and that, crucially for the case before the court, the particular phrase “officer of the United States” refers only to appointed positions, not the presidency.

If a majority of the court accepts Professor Tillman’s rationale, then Mr. Trump would be allowed to appear on the ballot. At issue is the meaning of Section 3 of the 14th Amendment, adopted after the Civil War, which bars people from holding office if they participated in an insurrection after having sworn to uphold the Constitution as an “officer of the United States.”

Professor Tillman, heavily bearded with black-rimmed glasses and a bookish demeanor, flew to the United States this week to watch the arguments. With Josh Blackman, who teaches at South Texas College of Law Houston, Professor Tillman submitted a friend-of-the-court brief and asked to participate in arguments, but the court declined.

Still, his hobbyhorse will be on the Supreme Court’s agenda, and it has drawn as much zealous backing as it has ferocious pushback.