Ah, article 4.
http://www.law.cornell.edu/constitution/articleiv
"Section 4.
The United States shall guarantee to every state in this union a republican form of government, and shall protect each of them against invasion; and on application of the legislature,
or of the executive (when the legislature cannot be convened) against domestic violence."
There it is.
The United States can intervene to act against domestic violence. I take that to mean that in the event of violence perpetrated, allowed or deliberately overlooked by a corrupt state government, as in the case in 1961 Alabama, the Feds can intervene.
JFK was in the right and all of these asshats who have been crying about it ever since don't know what they are talking about, as usual.
Excellent.
Dave