What transpires over the next weeks in a Washington, D.C., courtroom could serve as a coming attraction for the prosecution of a president. Lawyers for President Trump will no doubt be watching closely as prosecutors try to use a Civil War-era statute to convict a Yale Law graduate turned militia leader.  

Among the reams of indictments, charges, and convictions precipitated by the storming of the Capitol on January 6, 2021, the trial of Elmer Stewart Rhodes III and several other members of the Oath Keepers, a militia that he leads, for seditious conspiracy stands out for the gravity of its charges and the sweep of its accusations.  

Seditious conspiracy, labeled by a well-known law professor, Laurence Tribe, as “treason’s sibling,” is found at 18 U.S.C. § 2384. It was enacted in 1861, after the rash of secession by southern states. It had been contemplated after John Brown’s raid on the federal arsenal at Harper’s Ferry. It bears familial relation to the unmourned Sedition Act of 1798, which President John Adams signed but that President Jefferson allowed to expire.  

The Center for Strategic and International Studies defines the Oath Keepers as “an anti-government, right-wing political organization committed to supporting and defending their interpretation of the U.S. Constitution against all enemies.” They “associate today’s political environment with the British tyranny American colonialists faced before the American Revolution.”

The trial is set to kick off with opening statements on Monday. Jury selection was contentious, and Judge Amit Mehta rejected a request from Mr. Rhodes’s attorneys to move the trial from D.C. in the name of objectivity, wary of a jury pool for whom January 6 was local news. Politico described the pool as reflecting a “clubby professional set.”

That, at least, is how Secretary Clinton sees the state of play. She told CBS earlier this month that “I would not be honest if I didn’t say I think there was a seditious conspiracy against the government of the United States, and that’s a crime.” She went on to allege that the conspiracy was “led by Donald Trump, encouraged by Donald Trump.”

First, though, Mr. Rhodes. In the days before the 2020 election, he messaged his group that “we aren’t getting through this without a civil war. Too late for that. Prepare your mind, body, spirit.” That preparation led 12 of them, equipped with walkie talkies and tactical gear, to the U.S. Capitol on January 6. 

Mr. Rhodes is set to counter the seditious conspiracy charge with an equally esoteric statute, the 1807 Insurrection Act, which grants the president the power to summon militias in cases of national emergency. It has been invoked in response to everything from battles with Native Americans to disaster relief to efforts to tamp down riots.  

His lawyers argue that what “the Government contends was a conspiracy to oppose United States laws was actually lobbying and preparation” for President Trump to invoke the Insurrection Act. Prosecutors dismiss this as hypothetical and allege that Mr. Rhodes stashed guns, night-vision equipment, and sniper scopes outside of Washington, D.C., in preparation to stop the transfer of power. 

Mr. Rhodes himself did not enter the Capitol, but the government details how he stood on the perimeter and informed his allies that he and others would be “watching and waiting on the outside in case of worst case scenarios.” After the inauguration, Mr. Rhodes encouraged local cells to “organize local militias to oppose” the new Biden administration. 

Two members of the Oath Keepers have already pleaded guilty to the charge of seditious conspiracy, which carries a maximum prison sentence of 20 years. Members of another extremist group, the Proud Boys, have likewise been charged with seditious conspiracy. 

In pursuing convictions, prosecutors are likely to double as historians and look at a case that emerged from yet another fraught moment of American history: the trial of Aaron Burr and his confederates under the Constitution’s Treason Clause of Article III, Section 3.

The national parchment informs that “treason against the United States, shall consist only in levying war against them, or in adhering to their enemies, giving them aid and comfort.” Burr was acquitted in 1807, but the case law that ensued in the wake of the rogue Founding Father’s “western adventure,” or efforts to raise a fighting force to take territory from Spain, is now freshly relevant.    

A case that flowed from the machinations of Burr’s confederates reached the Supreme Court via habeas corpus, known as the “Great Writ.” Chief Justice Marshall warned that if there is “an assemblage of persons 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.”

In seeking to convict Mr. Rhodes — and, if the January 6 committee has its way, eventually Mr. Trump as well — the DOJ is likely to lean on this elastic characteristic of conspiracy, which is “an agreement between two or more people to commit an illegal act, along with an intent to achieve the agreement’s goal.” If the underlying crime is found, webs of culpability can ensnare distant participants, and conceivably those in the White House. 

For now, it is Mr. Rhodes, who served in the Army and clerked on the Arizona Supreme Court, who is in the prosecutorial crosshairs. His estranged wife, Tasha Adams, told the Associated Press that he was “going to achieve something amazing. He didn’t know what it was, but he was going to achieve something incredible and earth shattering.”