Actually there is precedent to an end-run around posse comitatus which can be used to federalize National Guard: Pres. Trump can cite the Insurrection Act - a pretty good fit for foreign nationals infiltrating and intentionally causing border chaos.
Watch some little insignificant pipsqueak judge in CA, OR, or HI pop up and declare DJTâs action “UNCONSTITUTIONAL”
Insurrection Act
The general purpose is to limit presidential power, relying on state and local governments for initial response in the event of insurrection
Better fit
The 2008 Defense Authorization Bill, repeals the changes made in the 2007 bill.
(1) The President may employ the armed forces, including the National Guard in Federal service, to--
(A) restore public order and enforce the laws of the United States when, as a result of a natural disaster, epidemic, or other serious public health emergency, terrorist attack or incident, or other condition in any State or possession of the United States, the President determines that--
(i) domestic violence has occurred to such an extent that the constituted authorities of the State or possession are incapable of maintaining public order; and
(ii) such violence results in a condition described in paragraph (2); or
(B) suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy if such insurrection, violation, combination, or conspiracy results in a condition described in paragraph (2).
(2) A condition described in this paragraph is a condition that--
(A) so hinders the execution of the laws of a State or possession, as applicable, and of the United States within that State or possession, 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 or possession are unable, fail, or refuse to protect that right, privilege, or immunity, or to give that protection; or
(B) opposes or obstructs the execution of the laws of the United States or impedes the course of justice under those laws.
To proclaim a state of insurrection is a necessary prerequisite if cascading powers, such as is found in 50 U.S.C. § 212 Confiscation of property employed to aid insurrection, are to be used.
Differences between old and new wording
The original wording of the Act required the conditions as worded in Paragraph (2), above, to be met as the result of
insurrection, domestic violence, unlawful combination, or conspiracy
The new wording of the Act, as amended, still requires the same conditions as worded in Paragraph (2), above, but those conditions could, after the changes, also be a result of
natural disaster, epidemic, or other serious public health emergency, terrorist attack or incident, or other condition
and only if
domestic violence has occurred to such an extent that the constituted authorities of the State or possession are incapable of maintaining public order.
By provisions in the amended act, Congress was granted the right to be informed immediately and every 14 days thereafter during the exercise of federal authority under these conditions.
I think that's the ticket which can be employed according to my non-legal mind reading it.