This is an open question. The judicial branch has authority, on paper. But without means of enforcing that authority, it cannot truly constrain the executive.
Congress has a jail, sure. But I and the comment I was responding to were regarding the judiciary.
To put a finer point on it: if the president orders somebody to do something in violation of federal law, and then pardons them, can the law be enforced?
Congress’s big hammer is impeachment. The smaller hammer is refusing to fund his administration. Between that and elections, that’s plenty of ways to keep the president in check.
Read the RFCP. ArtIII judges can absolutely empower people other than USMS to carry out legal orders such as service of process and enforcement of contempt orders.
This is an open question. The judicial branch has authority, on paper. But without means of enforcing that authority, it cannot truly constrain the executive.