If every gov't agency refuses to uphold the E.O., it becomes just another piece of paper...
But I might have been thinking of the Insurrection Act of 1797 instead. It has been retitled for the 21st century as "The Enforcement of the Laws to Restore Public Order Act” and codified in four sections of the US Code:
10 USC § 251 Federal Aid for State Governments
10 USC § 252 Use of Militia and Armed Forces to Enforce Federal Authority
10 USC § 253 Interference with State and Federal Law
10 USC § 254 Proclamation to Disperse
Of the four provisions, the most recent and the most powerful is 10 USC § 253, which was written in 2006.
It reads in part ".... The President, by using the militia or the armed forces, or both, or by any other means, shall take such measures as he considers necessary to suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy, if it-
1. .... so hinders the execution of the laws of that State, and of the United States within the State, that any part or class of its people is deprived of a right, privilege, immunity, or protection named in the Constitution and secured by law, and the constituted authorities of that State are unable, fail, or refuse to protect that right, privilege, or immunity, or to give that protection;
or 2. .... opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws."....
The authority is vested solely in the President. He does not need the invitation of state governors to intervene, nor does he need the approval of the Supreme Court. Older provisions of the Insurrection Act required either a governor or a judicial proceeding to authorize its use, but these limits were purposefully removed by Congress in § 253.
There is no time limit on the President’s activities. Older versions of the Insurrection Act limited the use of force to brief periods of time and then required legislative approval. Those limits, too, are also gone. The President is allowed to use any means that he (and again, he needs no one else) considers necessary. This includes using the armed forces (which enables him to bypass the Posse Comitatus Act) and using the militia (which we’ll discuss in more detail below).
The President’s ability to use force isn’t restricted to actual rebellion or insurgency. He can act against merely unlawful combinations and conspiracies. To be clear: If the President decides that a conspiracy has deprived people of a right and believes that authorities fail or refuse to protect the right, he can send in the troops.
In blunt terms, Congress has given the power to President Trump to proclaim:
“I, President Trump, have determined that a conspiracy has deprived 70 million Americans of their right to vote and that the other authorities are refusing to protect this right. I therefore order the suppression of this conspiracy by any means necessary.”
As long as the president has the military on his side (and he just replaced the Defense Secretary), it sounds like he can do this on his own without the courts, governors or the Congress.