Acting U.S. Defense Secretary Patrick Shanahan made his second trip to the U.S.-Mexico border on Saturday as the Pentagon looks to develop a longer-term plan to support President Donald Trump’s immigration policies.

Shanahan traveled to McAllen, Texas, to meet with officials and visit a migrant processing facility and Border Patrol station, two days after the White House announced Trump’s intention to nominate the former Boeing Co executive as defense secretary.

“We’re not going to leave until the border is secure,” Shanahan told about two dozen border patrol officials as hundreds of detained migrants waited in tents to be processed.

Shanahan was accompanied by another acting secretary, Kevin McAleenan, who leads the Department of Homeland Security (DHS) after a shake-up instigated by Trump, whose hard-line immigration policies have not stemmed a rising tide of migrants.

On Friday, the Pentagon said Shanahan approved the transfer of $1.5 billion to build more than 80 miles (130 km) of barriers on the border, part of a patchwork project after Trump failed to secure funding from Congress for a complete border wall.

Trump has been eager to have the U.S. military play a larger role on the border and, despite some criticism from lawmakers, Pentagon officials say they are looking to create a long-term plan for assistance.

Shanahan told a small group of reporters traveling with him that military assistance would not continue “indefinitely,” but that it would be in place longer than months.