The House select committee on the 6 January insurrection at the Capitol, according to chairman Bennie Thompson, should “not be reluctant” to include on its witness list Republicans including the minority leader, Kevin McCarthy, Jim Jordan and others who have knowledge of or may have been implicated in the attack.

Those who would be requested to testify spoke with Donald Trump before, during and after the assault, attended strategy meetings and held rallies to promote the 6 January “Stop the Steal” event, and are accused by Democrats of conducting reconnaissance tours of the Capitol for groups of insurrectionists.

But committee members and legal scholars are grappling to find precedent.

“I don’t know what the precedent is, to be honest,” said Adam Schiff.

There is one.

After a bloody insurrection was quelled, a congressional committee was created to investigate the organization of the insurrection, sources of funding, and the connections of the insurrectionists to members of Congress who were indeed called to testify. And did.

On the morning of 16 October 1859, John Brown led a ragtag band of armed followers in an attack on the US arsenal at Harpers Ferry, Virginia. His plan was to attract fugitive slaves to his battle, take refuge in the Allegheny mountains and conduct raids on plantations throughout the south, raising a slave army to overthrow the government and replace the constitution with one he had written.

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Nearly two weeks later, on 14 December, the Senate created the Select Committee to Inquire into the Late Invasion and Seizure of the Public Property at Harpers Ferry. Senator James M Mason of Virginia, the sponsor of the Fugitive Slave Act, was chairman. He appointed as chief prosecutor Jefferson Davis of Mississippi.

Davis was particularly intent on questioning Senator William H Seward of New York, the likely Republican candidate for president.

“I will show before I am done,” Davis said, “that Seward, by his own declaration, knew of the Harpers Ferry affair. If I succeed in showing that, then he, like John Brown deserves, I think, the gallows, for his participation in it.”