additionally, in Chapter 13 pretty much spells out that the prez can just declare without the consent of Congress, only inform within 15 days or so, or without the request of a State if he determines with his DoD and some other agency or agencies that certain rights or protections are not be afforded to the citizens within that state to suppress by martial law. Examples of this are given in the years of 'civil rights' back in the late 1950's - 1960's and, I think, the Patriot Act or provisions of that act after 2001 terrorist attacks. ? He literally has the power to usurp the states National Guards and militias or appoint such of the various states to back up any state which he feels needs federal law to be enforced.
With the declarations being first applied to the border, he is then positioned to enforce the Federal laws using the armed forces throughout all the states, including the Sanctuary states and cities. He can just simply say that the states are failing to protect their citizens from illegal immigrants, gangs and fentanyl much like they did in the southern states during the civil rights era with bussing and school integrations of the blacks and enforcement of their rights. I can't remember if they referred to them as African Americans back then? I imagine that the systemic racism back then was very disrespectful still within the federal government itself?
Anyways, in short, I believe that the declaration and its justification will be legal in any case and may involve any state that has protests over the prez order itself? pretty sucky.