President Trump declared a national emergency on Friday, February 15, saying that we are “going to confront the national security crisis on our southern border.”  The order is aimed at diverting previously allocated money to increase funding for expansion of the border wall. In the Q&A that follows, Stanford Law Professor Michael McConnell, a Constitutional Law expert and former circuit judge on the United States Court of Appeals for the Tenth Circuit, discusses the separation of powers, this latest presidential declaration of national emergency, and the law.

First, can you explain the separation of powers and why Congress holds the purse strings—and why it’s important to our democracy?

The power of the purse was the first and most important legislative power—the lever with which the British Parliament converted an absolute monarchy into a constitutional one. The text of the Constitution provides a double-barreled safeguard for the power of the purse: Article I, Section 8, gives Congress, not the President, power to tax and spend. Even more pointedly, Article I, Section 9, states that “No Money shall be drawn from the Treasury, but in consequence of Appropriations made by Law.” Republicans understood the importance of legislative control over expenditures when President Obama unilaterally spent $7 billion to subsidize health insurance companies that lost money under Obamacare, despite Congress’s refusal to appropriate the funds. The Republican House of Representatives challenged that expenditure in court (the first such case in American history), and the district court held that Obama’s expenditure was unlawful. The current line-up of opinion suggests that some people of both sides of the aisle think that different rules apply to presidents we like than to presidents we do not.

Congress did not agree with the president about the amount of funding required to expand the border wall. Do you know of a case in which a president declared a national emergency to get funding for something that Congress already voted not to fund?  This seems to be a clear-cut effort to not only circumvent Congress, but to overrule its powers of the purse.

It is not so clear cut. Congress has enacted statutes allowing the President to redirect funds in certain ways when he declares the existence of an emergency.  It is a close legal question whether yesterday’s action falls within the scope of emergency authority under those laws. 10 U.S.C. Section 2802 provides: “In the event of a declaration of war or the declaration by the President of a national emergency in accordance with the National Emergencies Act that requires use of the armed forces,” the executive may “undertake military construction projects, not otherwise authorized by law that are necessary to support such use of the armed forces.” The National Emergencies Act says simply that “[w]ith respect to Acts of Congress authorizing the exercise, during the period of a national emergency, of any special or extraordinary power, the President is authorized to declare such national emergency.” The acts contain no definition of “emergency,” seemingly leaving this to presidential discretion.

Why did Congress pass legislation in the 1970s to give the president this power? What was the intent?

Congress has passed some 123 statutes empowering the president to take actions on his own unilateral authority, upon declaration of an emergency, which otherwise would require legislative approval. The evident purpose is to allow these actions to take place immediately, when there is no time to go through the ordinary legislative process. Presumably Congress did not intend to give the president power to achieve longer-term goals that Congress opposes. But the actual language of the Emergencies Act is open-ended. According to the Brennan Center for Justice, presidents have declared emergencies under the statute fifty-nine times since 1979. Few of these had to do with war, many of them have lasted for decades, and it is doubtful that all of them would be regarded as “emergencies” in the ordinary sense of the word. In my personal opinion, hardening the porous border with Mexico does not appear to be an “emergency,” because the conditions there have existed with little change for decades—but one might have said the same thing about Reagan’s emergency order cutting off trade with South Africa’s apartheid regime, which had existed for half a century, or Clinton’s emergency order about narcotics trafficking.

Are you aware of a case in which the courts overturned the president’s use of emergency powers?

No court has overturned a president’s declaration of an emergency under the National Emergencies Act or any other statute empowering the President to declare a state of emergency. The Supreme Court overturned President Truman’s seizure of the steel mills during the Korean War, but in that case the President relied solely on his constitutional authorities and not, as here, a statutory grant of emergency powers.

California AG Becerra has said that he will challenge the president’s powers to fund the border wall with a national emergency declaration. How do you think the courts will view this challenge of presidential powers?

Becerra will have to get in line among many people who will challenge this decision. Unlike some recent legal controversies, there is no shortage of parties with legal standing to sue, including property owners affected by the wall and entities who would have received the grants that are now to be shifted to this project. The cases will present two legal issues: (1) Was the declaration of an emergency itself lawful under the Emergencies Act? and (2) Is the border wall a “military” construction project within the meaning of Section 2802 or a similar statute? (Remember, the relevant statutes only permit “military construction” projects “in support of” the armed forces.) As to the first issue, it is an open question whether the declaration of an emergency is judicially reviewable. The statute calls for congressional review of the presidential order, which may be an indication that Congress envisioned only a political remedy for potential abuse. And even if the declaration is judicially reviewable, the president should receive a high level of deference, as he received from the Supreme Court in the “travel ban” case. His own carelessness with language may be his biggest legal risk. Yesterday, for example, he stated that “I could do the wall over a longer period of time, I didn’t need to do this, but I’d rather do it much faster.” That statement could be construed by an unfriendly court as an admission that there was no “need” to act quickly, but only a preference.

I think it more likely that courts will focus on the second issue: whether the wall is a “military” construction project in support of the armed forces. The wall is not being built to fend off the Mexican army, but to bolster immigration enforcement. Congress has entrusted immigration enforcement to a civilian agency. True, President Trump has sent troops to the border to assist the immigration authorities, but as I understand it, they are only allowed to perform support roles; the Posse Comitatus Act prohibits the use of regular troops for mere law enforcement within the territory of the United States. If that is true, a court could hold that the wall is not in service of military needs as such.

What legislative remedy might Congress try if they oppose this declaration by President Trump?

All they have to do is pass a two-house resolution of disapproval. Because the President has power to veto such a resolution, however, it would have to carry two thirds of both Houses, which would not be easy. In return for not causing another government shut-down, the Senate Majority leader has promised to support the emergency order (no doubt gritting his teeth), making it unlikely there will be a veto-proof majority to enact a legally-binding resolution of disapproval. Politically, this is the mirror image of the ineffectual efforts of Congress to undo President Obama’s nuclear deal with Iran, which also appeared to lack majority support in Congress.

How do you see this developing—and why is it an important constitutional question?

First there will be efforts to enact a congressional resolution of disapproval. It will be interesting to see how many Republicans join in that effort. I suspect more than a few Republicans will conclude that even if the President’s emergency order is technically lawful, in spirit it is an end-run around the cherished congressional power of the purse and should be opposed for that reason even if the wall itself is a good idea. Assuming that the congressional effort is unsuccessful, perhaps because of a veto, many plaintiffs will file suit all over the country. Very likely, district courts will go both ways—some upholding the emergency order and some doing the opposite. Almost surely, one or more district courts will find the President’s actions to be unlawful under the emergency statutes and will issue preliminary injunctions. In the ordinary course, these would be subject to review in the courts of appeals, followed by certiorari in the Supreme Court—a process that could take two years or more. (Two years to decide whether we are in an emergency!) Very likely, the Solicitor General will ask the Supreme Court either to lift the preliminary injunctions pending review or to accelerate review, maybe by bypassing the courts of appeals, as just happened in the census case. It is difficult to predict whether the Supreme Court will do that.

Michael W. McConnell is the Richard and Frances Mallery professor of law and director of the Constitutional Law Center at Stanford Law School and a senior fellow at the Hoover Institution. He formerly served as a judge on the U.S. Court of Appeals for the 10th Circuit.