News that the Trump Administration considered using National Guard troops for immigration roundups drew strong reactions Friday, but it wouldn't be the first time they've been deployed to help enforce immigration laws. Our Bobby Cuza explains.

For most New Yorkers, their exposure to the National Guard has come at transit hubs like Penn Station, where troops patrol in support of counter-terrorism efforts, or during disasters like Hurricane Sandy, when they provide emergency relief.

"The National Guard is a force for good," said Kristen Rouse.

Often, they are also sent to war. Rouse, the founding director of the NYC Veterans Alliance, who served in the Army, Army Reserve, and New York National Guard, fought overseas in Afghanistan.

"A huge portion of New York's National Guard has been deployed overseas in Iraq or Afghanistan or adjacent areas," Rouse said.

National Guard troops are members of the Army or the Air Force. They train one weekend a month, plus a two-week training exercise each year.

While they can be activated by the president, they are generally under state control.

"We will also be activating the National Guard," Gov. Andrew Cuomo said in Oct. 2012.

That's why the Trump administration's draft memo notes that the governors of those states potentially affected would have to agree to allow troops to function as immigration officers.

That state authorization could be a way around federal law that prohibits the military from conducting law enforcement.

The National Guard has been deployed to the border before, both by Presidents George W. Bush and Obama, as well as by then-Texas Gov. Rick Perry in 2012.

"With this high influx of the illegal aliens, the gaps in the border have become bigger, and you now are the tip of the spear," Perry said to National Guard troops in August 2014.

But even in that case, troops were meant only to be a visible presence and to deter criminal activity.

Using them to arrest and detain immigrants across 11 states, as suggested in the draft memo, would be unprecedented.