President Trump may be about to declare a national emergency to pay for his border wall that Mexico isn’t paying for.

The legality of such a move is questionable: The National Emergencies Act of 1976 allows the president to declare national emergencies and another law, the Military Construction Codification Act of 1982 allows the president to do that and direct military construction projects that Congress did not otherwise approve—as long as the money comes out of the military construction budget. But, building a wall on the southern border might not be an entirely legitimate use of the armed forces, which are forbidden by law from participating in law enforcement functions inside the United States.

Even so, let’s say President Trump really could divert $5.7 billion from the military construction budget toward his wall. Where would that money come from?

In 2018, the total military construction budget for the entire Department of Defense (not including the Overseas Contingency Operations budget) was $6.4 billion. In FY 2019, DoD hopes to expand its construction budget—for projects such as barracks, shipyards, runways, control towers, garages, training facilities, and military family housing—to $8.9 billion. After paying for the wall—and assuming that the wall stayed on-budget—that would leave 36 percent of the budget for all of those projects.

As Thomas Sowell is fond of saying, there are no solutions in life, only tradeoffs. So what would we be trading for the wall?

The Army had planned to spend more than $300 million on new construction and improvements for military family housing overseas. As a non-mission-critical expense, it’s hard to imagine those outlays would survive the cuts necessary to build artistically designed steel slats.

Two on-base middle schools the DoD had planned would have cost just shy of $163 million. That’s enough to build about 57 miles of steel slats along the 2,000-mile border. Maybe you think fence for 2.8 percent of the border is worth two middle schools for the children of American service members. Maybe you don’t. You probably don’t.

In Germany, the DoD had planned to spend nearly $320 million to replace a medical center at the Rhine Ordnance Barracks near Ramstein Air Base. During the Iraq and Afghanistan wars, Germany was often the first stop for wounded soldiers in need of emergency surgery. Many, many lives were saved there. And American forces are still deployed to Iraq, Jordan, Syria, and Afghanistan. Surely the president who claimed “nobody has been better at the military” wouldn’t sacrifice the health and well-being of our troops in conflict zones.

Or would he?