Article 1, Section 1
All legislative Powers herein granted shall be vested in a Congress of the United States, which shall consist of a Senate and House of Representatives
Article 3, Section 5
he shall take Care that the Laws be faithfully executed,
Executive Orders are kinda iffy but an understandable thing to have.... so sure, I can take them as legal. However, making sure the laws are faithfully executed
DOES NOT MEAN WRITING NEW LAWS.
Given the millions of laws on the books, I'm sure you could find something that 'must be enforced or ermagherd the oceans will fall out of the sky'...
Note, I have similar qualms from judges who attempt to legislate from the bench