Here's the kicker for the Posse act

In the mid-20th century, the administration of President Dwight D. Eisenhower used an exception to the Posse Comitatus Act, derived from the Enforcement Acts, to send federal troops into Little Rock, Arkansas, during the 1957 school desegregation crisis. The Arkansas governor had opposed desegregation after the U.S. Supreme Court ruled in 1954 in the Brown v. Board of Education that segregated public schools were unconstitutional. The Enforcement Acts, among other powers, allow the president to call up military forces when state authorities are either unable or unwilling to suppress violence that is in opposition to the constitutional rights of the people.

Unable or Unwilling… think sanctuary cities

https://en.wikipedia.org/wiki/Posse_Comitatus_Act