SAN DIEGO (AP) — After a contentious standoff between the state and federal government, California National Guard troops started training Thursday with the U.S. Customs and Border Patrol to be camera operators, radio dispatchers, and to fill other support roles.

President Donald Trump ordered National Guard troops to deploy to the U.S.-Mexico border to help federal authorities combat illegal immigration and drug trafficking.

California's all-Democratic leadership has positioned the state as a national leader in battling the Trump administration, especially on immigration issues. Government leaders at the state level and in big cities have condemned mass raids and deportation efforts, President Donald Trump's call for a border wall with Mexico and Attorney General Jeff Sessions' "zero tolerance" order to prosecute people caught illegally entering the United States for the first time.

Gov. Jerry Brown agreed to contribute 400 troops to the National Guard's deployment to the Mexican border to help go after drugs, guns and criminal gangs — not immigrants.

The governor has said under the terms of the agreement the state reached with the Trump administration, the Guard cannot handle custody duties for anyone accused of immigration violations, build border barriers or have anything to do with immigration enforcement.

Some troops could start their new jobs as soon as Sunday, which will free up agents to patrol the Mexican border but keep National Guard members away from the international line so they do not have contact with migrants.

Maj. Kimberly Holman told The Associated Press that some of the 250 troops who volunteered for the call to help Border Patrol agents started their on-the-job training Thursday after meeting their Border Patrol supervisors in San Diego.

"This will free up the green shirts — the badged agents — and get them out on line," Holman said, adding that troops volunteered for the mission because they want to keep California safe.

"Nobody has been ordered to come here," she said. "Everyone is here by choice and has said, 'I would like to support this mission.'"

So far, 250 are in place but more troops may be added as the Border Patrol needs them, Holman said.

William Rogers, supervisory Border Patrol agent for the San Diego sector, said troops are being put in jobs that will keep them away from migrants. For example, he said National Guard camera operators will work monitoring video inside Border Patrol facilities and will not be assigned to manning a camera from a vehicle parked at the international line.

He said the added manpower for jobs suchas dispatching radio calls and maintaining vehicles will mean agents can also focus more on investigative work.

"I think people really underestimate the help that the Guardsmen will provide," Rogers said. "I actually think this also will provide a huge sort of morale boost to agents by seeing Guardsmen enthusiastically doing their jobs."

The troops, who will also work in neighboring Imperial County, are expected to stay until at least Sept. 30.

National Guard troops are also assisting agents in three other U.S. states bordering Mexico — Arizona, New Mexico and Texas — all governed by Republicans.