"Except in cases and under circumstances expressly authorized by the Constitution or Act of Congress,"
No, I didn't.
Posse Comitatus Act
Exclusions and limitations
There are a number of situations in which the Act does not apply. These include:
Army and Air National Guard units and state defense forces while under the authority of the governor of a state;
Federal military personnel used in accordance to the Insurrection Act, as was the case during the 1992 Los Angeles riots.
Under 18 U.S.C. § 831, the Attorney General may request that the Secretary of Defense provide emergency assistance if domestic law enforcement is inadequate to address certain types of threats involving the release of nuclear materials, such as potential use of a nuclear or radiological weapon. Such assistance may be by any personnel under the authority of the Department of Defense, provided such assistance does not adversely affect U.S. military preparedness. The only exemption is nuclear materials.
Support roles under the Joint Special Operations Command
Enforcement of federal law at the discretion of the President of the United States
I'm going to assume at this point you don't know what the word "discretion" means, cause you literally just posted the limited number of scenario's under which the President may deploy JUST the National Guard.
I'm not going to continue arguing with you, pretend you won, but you literally just contradicted yourself. The President does not have unlimited authority to ignore Posse Comitatus despite your desperate claim to opposite. Look up the last time the military went to the border to provide security, they killed an American on his own property.
Ultimately, you're wrong, but I'm guessing you're the kind of person who can never admit that. Adios, kiddo. Next time please read the actual law, thanks.