General Discussion

Recent court rulings have established that federal courts can block a president from federalizing a state's National Guard if the specific legal criteria for federal intervention are not met.
A governor can challenge the federalization in court, and courts can support the governor's objection.

2025 cases):
In several cases involving the Trump administration's attempts to deploy the National Guard in California, Oregon, and Illinois, federal courts and an appellate court ruled against the administration.
A federal judge in Oregon ruled that the President "did not have a lawful basis to federalize the National Guard" for the purposes intended.
Courts determined that the circumstances in these cases (protests and immigration enforcement) did not meet the stringent criteria of an "insurrection, rebellion, or obstruction of federal law" as required by the relevant statute (10 U.S.C. § 12406).

The U.S. Supreme Court denied an emergency request by the Trump administration to keep troops in Illinois, upholding a lower court's block on the deployment.

Posse Comitatus Act: Courts note that when federalized, the Guard becomes subject to the Posse Comitatus Act, which generally prohibits the use of federal military forces for domestic law enforcement unless an exception (like the Insurrection Act) is lawfully invoked.

Governor's Authority: These rulings reinforced the principles of federalism, confirming that state governors retain significant authority over their National Guard units when they are not lawfully federalized.