DENVER — A conservative activist who served as a chairman of a “Veterans for Trump” coalition in New Hampshire was one of 14 people charged on Thursday by the Justice Department in connection with the armed showdown over federal control of grazing lands led by the Nevada rancher Cliven Bundy.

The federal indictments were part of an expanding criminal case that now includes charges against 19 members of the Bundy family and their allies stemming from the weekslong standoff in 2014 over Mr. Bundy’s illegal grazing on federal lands. During the confrontation, about 50 Bundy supporters from around the country gathered at the family’s ranch in Bunkerville, Nev., to prevent the Bureau of Land Management from confiscating Mr. Bundy’s approximately 500 cattle, whom he had been letting loose on federal land for decades, accruing more than $1 million in grazing fees.

Among those people arrested on Thursday was Gerald A. DeLemus, 61, of Rochester, N.H, a former Marine who in July 2015 was named to a New Hampshire veterans group supporting Donald J. Trump, the Republican front-runner. Prosecutors said that, in actions well before Mr. Trump’s campaign, Mr. DeLemus had acted as a “gunman and midlevel organizer” during the standoff in 2014 in Nevada.

Mr. Bundy and four others — including two of his sons, Ryan and Ammon — were indicted last month on charges they carried out a “massive armed assault” on the federal officers who tried to confiscate Mr. Bundy’s cattle; Bureau of Land Management rangers pulled back from the confrontation. This winter, Ammon and Ryan Bundy led a weekslong armed takeover of a wildlife refuge in eastern Oregon, and are among several facing separate criminal charges in that case.