An executive order directs the executive branch
Executive orders are written presidential directives used to manage operations of the federal government. Their authority must ultimately rest on the Constitution or powers Congress has granted by statute.
That makes them powerful administrative instruments, but not substitutes for legislation. A president cannot use an executive order to create authority that the executive branch does not possess.
Implementation determines how much changes
Agencies often have to translate presidential direction into rules, guidance, enforcement priorities or administrative practice. Appropriations, statutory duties and procedural requirements can limit how quickly or extensively that happens.
The practical power of an order therefore depends partly on the legal authority and administrative machinery available to carry it out.
The order is not the last word
Federal courts can review executive action when a dispute is properly before them. Congress can change underlying statutes or funding, subject to the ordinary legislative process, and later presidents can revoke or amend many predecessor orders.
The useful question is not whether executive orders are powerful in the abstract, but which legal authority supports a particular order and which institutions retain the ability to constrain it.