Patrick Shanahan, the acting US Secretary of Defense, said hours after Donald Trump’s emergency declaration that he could refuse to direct billions of dollars in Pentagon funds Trump is relying on to build a wall on the US’s southern border.

“Very deliberately we have not made any decisions,” about how the defense department will respond to Trump’s declaration, Shanahan told reporters as he returned from a trip to Afghanistan and Iraq. “There’s been no determinations by me” that a wall is necessary, he said, while making it very clear that he believes he has the authority to determine how any military funds will be spent and military personnel deployed.

Trump said Feb. 15 that he planned to use $6 billion in Pentagon funds, targeted for military construction and counter-drug activities, to build the wall. “All of this money has been assigned for other purposes, so it really then comes to what…are you going to trade off, because when you say tradeoff, it really is a tradeoff,” Shanahan said in the press conference.

His response is part of a coordinated effort by the Pentagon to push back on Trump on the issue. The Department of Defense “is authorized to determine whether border barriers are necessary to support the use of the armed forces in this emergency and whether to redirect funds for unobligated military construction funds to support that,” the Pentagon said in a statement after Trump’s announcement. On Jan. 29, Pentagon officials testified to Congress that they didn’t see the situation on the southern border as an emergency.

Asked Feb. 16 whether he, personally, had the “discretion” to determine how much money went to the wall or if he was required to acquiesce to the White House’s demands, Shanahan told reporters “No, I’m not required to do anything.” He hasn’t spoken to the president this weekend, he said.

Shanahan said he asked the “Northern Command,” the Pentagon division responsible for US homeland security, to work with the Joint Staff on a “mission analysis of the border” a few weeks ago. He said he asked them: “Based on the influx of either drugs or people, how would you assign DOD personnel, guard or reserve, to support the Department of Homeland Security broadly.” He will review that analysis this week, he said.

Shanahan highlighted the press interaction in a tweet, calling it a “great conversation,” a rare positive sentiment about the media from a Trump administration official:

The emergency declaration faces challenges in court from the ACLU and Public Citizen, an advocacy group. Both houses of Congress are also planning resolutions to stop it, Jim Jordan, the Ohio Republican, said Feb. 17.