A president cannot create policies that violate constitutional rights. For example, Mr. Fidell said, the president could not block anyone of a specific race or religion from becoming a SEAL because of equal protection and First Amendment rights. A case challenging the president’s decision to bar transgender recruits from joining the military is working its way through the courts.
A president also cannot order the military to do something that violates a law enacted by Congress, such as the law that repealed the Don’t Ask, Don’t Tell policy, which barred gay troops from serving openly in the military.
But those two constraints leave a broad thoroughfare, crowded with ships, fighter jets and nuclear weapons, where the president has considerable discretion.
“Think of the implications,” Mr. Fidell said. “I suppose it is possible he could tell the Navy who should be a pilot. And if the guy in charge didn’t like it, he could fire him.”
The president’s power over the military is no mistake. Founding fathers knew the executive would need broad authority in war. But the real boundaries of what a president can do as a commander in chief in the day-to-day operations of the armed forces have never been tested, experts say, because since the beginning of the republic the presidency has given the military broad deference in how it runs its affairs.
“The Constitution is a very brief document; it leaves a lot unsaid. So for centuries the president and the military have had to rely on mutual understanding,” said Thomas Bruneau, who taught national security at the Naval Postgraduate School. The president makes broad strategic and political decisions about military power, he said, and the military generally makes decisions on how those decisions will be executed, and by whom.
“This level of intervention at such a low level? I’ve never seen it,” Mr. Bruneau said.
To be sure, presidents have sometimes involved themselves in the minutiae of making war. President Lyndon B. Johnson, for example, personally approved targets for B-52 bombing runs in Operation Rolling Thunder, during the Vietnam War.