The Pentagon is ready to provide more troops or whatever else is needed to seal the Mexican border, if President Donald Trump declares a national emergency, Acting Secretary of Defense Patrick M. Shanahan told reporters Tuesday. “The president would declare national emergency and then we would do the planning and do the recommendation on how the military could support the request,” he said. It would likely involve more troops and possibly extra aviation to help stop illegal crossings. “It’s really around this mission of monitoring, surveilling and detection. If we detect activity, that’s when we notify Customs and Border Protection, and they do their apprehension.”

Under existing law, the military could use military construction funds to support the effort, if they haven’t already been appropriated for something else.“This is not something that’s unique or unprecedented,” he said, chiding the reporters to “do their homework” on the “number of national emergencies” that have been declared previously by U.S.presidents.

The Pentagon is already preparing to send “several thousand” more troops to the border, Shanahan said, in answer to a DHS request for more help on surveillance and laying down more concertina wire. Currently, there are roughly 2,300 national guard troops at the border, assisting with administrative, logistics and transportation, and 2,350 active duty troops whose mission has been extended through September, according to Pentagon spokesman Lt. Col. Jamie Davis. He said that’s down from a high water mark of 5,900 active duty troops who were deployed there last fall.

—Kim Dozier