These are powers that Congress has voted on and deletated to the President. If they choose, they could revoke these powers.
If Trump had been a different sort of guy, he might have encouraged Congress to remove these powers and signed the bill. That would have been a big deal if the Presidency goes to the Democrats.
(Also from The Atlantic)
Nonetheless, some legal scholars believe that the Constitution gives the president inherent emergency powers by making him commander in chief of the armed forces, or by vesting in him a broad, undefined “executive Power.” At key points in American history, presidents have cited inherent constitutional powers when taking drastic actions that were not authorized—or, in some cases, were explicitly prohibited—by Congress. Notorious examples include Franklin D. Roosevelt’s internment of U.S. citizens and residents of Japanese descent during World War II and George W. Bush’s programs of warrantless wiretapping and torture after the 9/11 terrorist attacks. Abraham Lincoln conceded that his unilateral suspension of habeas corpus during the Civil War was constitutionally questionable, but defended it as necessary to preserve the Union.
The Supreme Court has often upheld such actions or found ways to avoid reviewing them, at least while the crisis was in progress. Rulings such as Youngstown Sheet & Tube Company v. Sawyer, in which the Court invalidated President Harry Truman’s bid to take over steel mills during the Korean War, have been the exception. And while those exceptions have outlined important limiting principles, the outer boundary of the president’s constitutional authority during emergencies remains poorly defined.