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.

Brown became notorious as pro- and anti-slavery forces fought over how Kansas would be admitted to the Union. Brown committed a massacre and rampaged out of control. Radical abolitionists idealized him as an avenging angel of Puritan virtue. Some of the most prominent and wealthiest, known as the Secret Six, funded him without being completely clear about how the money was going to be used.

Brown confided his plan on the eve of his raid to the great Black abolitionist Frederick Douglass and asked him to join. Douglass told him he would be entering “a perfect steel-trap and that once in he would never get out alive” and refused the offer. Brown was undeterred.

Within hours of the assault Brown and his band were cornered in the engine room of the armory, surrounded by local militia. Then the marines arrived under the command of Col Robert E Lee and Lt Jeb Stuart. At Brown’s public trial, his eloquent statements against slavery and hanging turned him into a martyr. John Wilkes Booth, wearing the uniform of the Richmond Grays and standing in the front ranks of troops before the scaffold on which Brown was hanged on 2 December, admired Brown’s zealotry and composure.

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.”

In early May 1858, Hugh Forbes, a down-at-heel soldier of fortune, a Scotsman who fought with Garibaldi in the failed Italian revolution of 1848, a fencing coach and a translator for the New York Tribune, knocked on Seward’s door with a peculiar tale of woe. He had been hired by Brown to be the “general in the revolution against slavery”, had written a manual for guerrilla warfare, but had not been paid. Seward sent him away and forgot about him.

Forbes wandered to the Senate, where he told his story to Henry Wilson, a Republican from Massachusetts. Wilson, who later became Ulysses S Grant’s vice president, was alarmed enough to write to Dr Samuel Gridley Howe, a distinguished Boston physician and reformer, founder of the first institution for the blind, and Massachusetts chairman of the Kansas committee. Wilson relayed that he had heard a “rumor” about John Brown and “that very foolish movement” and that Howe and other donors to the Kansas cause should “get the arms out of his control”.

But Howe, a member of the Secret Six, continued to send Brown money.

The investigating committee called Seward and Wilson. On 2 May 1860, Seward testified that Forbes came to him, was “very incoherent” and told him Brown was “very reckless”. Seward said he offered Forbes no advice or money, and that Forbes “went away”.

Davis pointedly asked Seward if he had any knowledge of Brown’s plan to attack Harpers Ferry.

Seward replied: “I had no more idea of an invasion by John Brown at that place, than I had of one by you or myself.”

Wilson also testified, producing his correspondence with Howe, his recollection of strangely encountering Brown at a Republican meeting in Boston, and denying any knowledge of Brown’s plot. Other witnesses were subpoenaed and warrants were issued for the arrest of those who failed to appear. Howe testified that he knew nothing in advance of the raid.

The Senate committee concluded its report citing the fourth section of article four of the constitution: “The United States shall guaranty to every State in this Union a republican form of government, and shall protect each of them against invasion, and, on the application of the legislature or of the executive, (when the legislature cannot be convened,) against domestic violence.”

Eight months after submitting the report, Davis was sworn in as president of the Confederacy, assuming command of the greatest insurrection against the United States in its history.

His legacy as a senator before the civil war, however, established the precedent of a congressional committee calling members of Congress to testify about their knowledge of or participation in an insurrection: a precedent that can be used to investigate one in which for the first time the Confederate flag was carried through the Capitol.

• Sidney Blumenthal, former senior adviser to President Bill Clinton and Hillary Clinton, has published three books of a projected five-volume political life of Abraham Lincoln: A Self-Made Man, Wrestling With His Angel and All the Powers of Earth