WASHINGTON — The N.A.A.C.P. on Tuesday morning filed a federal lawsuit against former President Donald J. Trump and his personal lawyer Rudolph W. Giuliani, claiming that they violated a 19th century statute when they tried to prevent the certification of the election on Jan. 6.
The civil rights organization brought the suit on behalf of Representative Bennie Thompson, Democrat of Mississippi. Other Democrats in Congress — including Representatives Hank Johnson of Georgia and Bonnie Watson Coleman of New Jersey — are expected to join as plaintiffs in the coming weeks, according to the N.A.A.C.P.
The lawsuit contends that Mr. Trump and Mr. Giuliani violated the Ku Klux Klan Act, an 1871 statute that includes protections against violent conspiracies that interfered with Congress’s constitutional duties; the suit also names the Proud Boys, the far-right nationalist group, and the Oath Keepers militia group. The legal action accuses Mr. Trump, Mr. Giuliani and the two groups of conspiring to incite a violent riot at the Capitol, with the goal of preventing Congress from certifying the election.
The suit is the latest legal problem for Mr. Trump: New York prosecutors are investigating his financial dealings; New York’s attorney general is pursuing a civil investigation into whether Mr. Trump’s company misstated assets to get bank loans and tax benefits; and a Georgia district attorney is examining his election interference effort there.
Jason Miller, an adviser to Mr. Trump, noted in response to the lawsuit that the Senate had acquitted the former president of the article of impeachment on inciting an insurrection. The Senate voted 57-43, falling short of the two-thirds majority required to convict.
“President Trump did not plan, produce or organize the Jan. 6 rally on the Ellipse. President Trump did not incite or conspire to incite any violence at the Capitol on Jan. 6,” Mr. Miller said in a statement on Tuesday.
In the lawsuit, Mr. Thompson said he was forced to wear a gas mask and hide on the floor of the House gallery for three hours while hearing “threats of physical violence against any member who attempted to proceed to approve the Electoral College ballot count.” Mr. Thompson also heard a gunshot, according to the suit, which he did not learn until later had killed Ashli Babbitt, one of the rioters in the Capitol lobby.
Mr. Thompson is seeking compensatory and punitive damages in the lawsuit filed in Federal District Court in Washington. The suit does not include a specific financial amount.
Mr. Thompson, 72, claims he was put at an increased health risk by later being required to shelter in place in a cramped area that did not allow for social distancing. The lawsuit notes that Mr. Thompson shared confined space with two members of Congress who tested positive for the coronavirus shortly after the attack at the Capitol.
In an interview on Monday, Mr. Thompson said he would not have brought the suit against Mr. Trump if the Senate had voted to convict him in last week’s impeachment trial.
“I feared for my life,” Mr. Thompson said. “Not a day passes that I don’t think about this incident. I was committed to seeing justice brought to this situation.”
He added: “This is me, and hopefully others, having our day in court to address the atrocities of Jan. 6. I trust the better judgment of the courts because obviously Republican members of the Senate could not do what the evidence overwhelmingly presented.”
Mr. Thompson said he had already received a second dose of a Covid vaccine by Jan. 6 and therefore did not quarantine after his close contacts with colleagues who tested positive. But he noted, “There were a number of members who were very concerned about being housed in those numbers with people refusing to wear masks.”
Both Democratic and Republican members of Congress have recently raised the prospect of Mr. Trump being held accountable in the courts for the riot. Senator Mitch McConnell, the Republican leader, voted to acquit Mr. Trump in the impeachment trial but then appeared to encourage people to take their fight to the courts.
“He didn’t get away with anything, yet,” Mr. McConnell said at the trial’s conclusion, noting: “We have a criminal justice system in this country. We have civil litigation.”
Derrick Johnson, president of the N.A.A.C.P., said the decision to seek compensatory and punitive damages was rooted in a history of tools that have worked to fight back against white supremacy.
“The Southern Poverty Law Center filed a lawsuit against the Ku Klux Klan that bankrupted a chapter,” he said, referring to a 2008 judgment against a Kentucky-based Klan outfit that ordered the group to pay $2.5 million in damages. “This is very similar. If we do nothing, we can be ensured these groups will continue to spread and grow in their boldness. We must curb the spread of white supremacy.”
While much of the focus of the impeachment trial rested on how the violent mob was threatening former Vice President Mike Pence as well as congressional leaders like the House speaker, Nancy Pelosi, N.A.A.C.P. officials said the attack was deeply rooted in racial injustice.
“Underlying this insurrection were the actions of folks who were challenging the voices of people of color,” said Janette McCarthy Louard, deputy general counsel of the N.A.A.C.P. “If you look at whose votes were being challenged, these came from largely urban areas. The votes of people of color were being challenged.”
The suit, for instance, charges Mr. Giuliani with attempting to reject “the votes cast by voters in Detroit, the population of which is 78 percent African-American.” It also says Mr. Giuliani inaccurately claimed there was fraud in voting in Milwaukee and Madison, Wis., “both of which have large African-American populations.”
Joseph M. Sellers, a partner at the civil rights law firm Cohen Milstein Sellers & Toll, which jointly filed the case, said the lawsuit named Mr. Trump in his personal capacity because his conduct challenging another branch of government to do its job falls outside the official duties of the president.
“He was engaging in conduct that is so far outside any remotely legitimate scope of his presidential duties,” Mr. Sellers said. “He no longer has the immunity of the president.”