A member of the far-right Oath Keepers extremist group has become the first to admit to engaging in seditious conspiracy on Jan. 6, 2021, to keep President Biden from taking office.

Joshua James, 34, of Arab, Ala., pleaded guilty in federal court in Washington on Wednesday to helping lead a group that prosecutors say sent two tactically equipped teams into the Capitol and organized a cache of weapons in a hotel just outside the city. He also pleaded guilty to one count of obstructing an official proceeding, and he may face the stiffest sentence of any Jan. 6 defendant so far, according to preliminary sentencing guidelines.

As part of his plea, James agreed to cooperate with federal investigators, including testifying in front of a grand jury.

James, an Army veteran who was injured fighting in Iraq, was indicted on the sedition charge in January along with 10 others, including Oath Keepers founder and leader Stewart Rhodes. James faced multiple felony counts of obstructing the formal count of the electoral college, as well as assaulting a D.C. police officer during his time inside the Capitol. He was also accused of tampering with documents to destroy his communications with other Oath Keepers. Prosecutors agreed to dismiss the charges other than the seditious conspiracy and obstruction counts. Both charges carry a maximum 20-year prison term. No defendant has yet been sentenced to a maximum term.

James appeared in court virtually from Alabama; he was released on GPS monitoring in April over government objections. U.S. District Judge Amit P. Mehta said the sentencing guidelines for both the sedition and the obstruction charge were calculated to a range of 87 to 108 months in prison. The range is advisory, and both sides can ask for the judge to go above or below the range at sentencing.

The longest sentence any Jan. 6 defendant has received so far is 63 months for Robert S. Palmer, who admitted to hurling a fire extinguisher, a plank and a long pole at officers.

Five other Oath Keepers, apart from the 11 charged with seditious conspiracy, have already pleaded guilty and agreed to cooperate with the government. But James is the first to plead to sedition, a rarely used and politically significant crime of conspiring against the U.S. government.

James did not make any statements in court other than to answer the judge’s questions. No sentencing date was set, which Assistant U.S. Attorney Troy Edwards Jr. said was done to enable James to provide his cooperation before the hearing.

The plea marks the first successful use of a sedition charge by federal prosecutors in decades. Federal law defines seditious conspiracy as two or more people who “conspire to overthrow, put down, or to destroy by force the Government of the United States,” or act “by force to prevent, hinder, or delay the execution of any law of the United States.”

James’s defense attorneys, Chris Leibig and Joni Robin, said in a statement that he pleaded not to the first part of the law but only the second part, “preventing, hindering or delaying, by force, a federal law.” ...