In his first six months in office, President Donald Trump has overseen the deployment of nearly 20,000 federal troops on American soil, including personnel from the National Guard, the Army, the Navy, the Air Force, and the Marines, according to the Pentagon’s public statements.

But the true number of troops deployed may be markedly higher. When asked directly, the Army said it has no running tally of how many troops have been deployed. These federal forces have been operating in at least five states — Arizona, California, Florida, New Mexico, and Texas — with more deployments on the horizon, all in service of the Trump administration’s anti-immigrant agenda.

Experts say military involvement in domestic anti-immigrant operations undermines American democracy and has nudged the United States closer to a genuine police state.

“If the president can use the military as a domestic police force entirely under his control, it can be used as a tool of tyranny and oppression.”

“This level of involvement of the military in civilian law enforcement in the interior of the country is unprecedented — and really dangerous,” said Elizabeth Goitein, senior director of the Brennan Center’s liberty and national security program, who told The Intercept that recent deployments violated the Posse Comitatus Act, a bedrock 19th-century law seen as fundamental to the democratic tradition in America which bars federal troops from participating in civilian law enforcement.

She added: “If the president can use the military as a domestic police force entirely under his control, it can be used as a tool of tyranny and oppression. We’ve seen it all around the world and throughout history.”

The norms surrounding the use of military force within U.S. borders are eroding, and the executive branch is operating with free rein, emboldened by a legislature and judiciary seemingly uninterested in curtailing its actions.

These soldiers have been sent to patrol the border, put down popular protest against Immigration and Customs Enforcement operations, participate in ICE raids, and assist in immigration enforcement missions from coast to coast. Here, to the extent of what is known so far, is what they’ve been up to.

President Donald Trump began the further militarization of America on his first day back in office. “Our southern border is overrun by cartels, criminal gangs, known terrorists, human traffickers, smugglers, unvetted military-age males from foreign adversaries, and illicit narcotics,” Trump announced on January 20, directing the military to “assist the Department of Homeland Security in obtaining full operational control of the southern border.”

Despite the fact that Trump’s fearmongering was his typical hyperbole, more than 10,000 troops are deploying or have deployed to the southern border, according to U.S. Northern Command, or NORTHCOM, which oversees U.S. military activity from Mexico’s southern border up to the North Pole.

Under the direction of NORTHCOM, military personnel — including soldiers from the Fourth Infantry Division at Fort Carson in Colorado, one of the Army’s most storied combat units — have deployed under the moniker Joint Task Force-Southern Border, or JTF-SB, since March, bolstering approximately 2,500 service members who were already supporting U.S. Customs and Border Protection’s border security mission.

One-third of the U.S. border is now completely militarized due to the creation of four new national defense areas, or NDAs: sprawling extensions of U.S. military bases patrolled by troops who can detain immigrants until they can be handed over to Border Patrol agents.

The Air Force is responsible for the recently created South Texas NDA, which encompasses federal property along 250 miles of the Rio Grande River. The Navy controls the Yuma NDA, which extends along 140 miles of federal property on the U.S.–Mexico border near the Barry M. Goldwater Air Force Range in Arizona.

The New Mexico NDA, created in April, spans approximately 170 miles of noncontiguous land along that state’s border, serving as an extension of the Army’s Fort Huachuca. Another NDA was created in May in West Texas and covers approximately 63 miles of noncontiguous land between El Paso and Fort Hancock, serving as an extension of the Army’s Fort Bliss.