If we were President Trump’s lawyers — a stretch to be sure — we would be reading up on a Supreme Court case called Ex Parte Bollman. It centers on a conspiracy of treason in respect of Aaron Burr. A United States magistrate will today weigh whether to deny bail to the leader of the Oath Keepers, Elmer Stewart Rhodes III, on a charge — seditious conspiracy — that Harvard’s Laurence Tribe calls “treason’s sibling.”

Which is where Bollman comes in. It was the first treason ruling by the Supreme Court. Sedition is a lesser crime than treason, which the Constitution confines to levying war against the United States or adhering to their enemies, giving them aid and comfort. Yet if Mr. Rhodes et al are convicted, they could spend decades in prison. And so, Bollman warns, could Mr. Trump.

Prosecutors’ intentions to ensnare Mr. Trump in seditious conspiracy charges emerged in court filings for a defendant named Brandon Straka. In Justice Department interviews with Mr. Straka, his lawyer says, “the government was focused on establishing an organized conspiracy” between Mr. Straka, “President Donald J. Trump, and allies of the former president to disrupt the joint session of Congress on Jan. 6.”

This suggests the intention of prosecutors to “reach beyond those who took part in the melee on Jan. 6 and seek to build a case against Mr. Trump,” along with “his allies who helped inspire the violence that day,” the New York Times last week observed. If so, prosecutorial efforts to prove that Mr. Rhodes committed seditious conspiracy will serve as a preview of coming attractions for Mr. Trump.

Prosecutors say Mr. Rhodes plotted “by force to prevent, hinder, and delay the execution” of American law. The charges echo Bollman, which involved two of Burr’s confederates, who were in the dock for conspiring with him. They were acquitted by Chief Justice Marshall because the war Burr contemplated wasn’t levied. It’s not clear to us that the Oath Keepers — and Mr. Trump — will be so lucky.

In Bollman, Marshall reckoned, the absence of an attack on the United States by Burr and his conspirators meant there was no treason. “However flagitious may be the crime of conspiring to subvert by force the government of our country,” the chief justice wrote, “such conspiracy is not treason.” Yet it was “not the intention of the Court to say that no individual can be guilty of this crime who has not appeared in arms against his county.”

“On the contrary,” Marshall wrote, in words that resonate today, “if war be actually levied — that is if a body of men be actually assembled for the purpose of effecting by force a treasonable purpose — all those who perform any part, however minute or however remote from the scene of action, and who are actually leagued in the general conspiracy, are to be considered as traitors.”

Marshall’s reasoning in Bollman was echoed — intentionally, we suspect — by Attorney General Garland in his remarks on the anniversary of January 6. He warned the Justice Department was “committed to holding all January 6th perpetrators, at any level, accountable under law — whether they were present that day or were otherwise criminally responsible.”

Bollman and Swartwout went free because Marshall understood that treason requires “an actual assembling of men for the treasonable purpose to constitute a levying of war.” Mr. Rhodes and his associates, prosecutors say, “equipped themselves with a variety of weapons, donned combat and tactical gear,” and were poised “to take up arms” to further their “plot to stop the lawful transfer of presidential power.”

It’s not our intention to suggest that Mr. Trump — or Mr. Rhodes and the other Oath Keepers — intended or conspired to commit sedition. We doubt Mr. Trump did, but await to see what evidence is adduced. The point here is that if the government prevails in proving seditious conspiracy against anyone, Bollman suggests the courts don’t have to worry about the fact that Mr. Trump was not at the Capitol.