The U.S. Constitution places primary responsibility for the holding of elections in the hands of the individual states. The maintenance of peace, conduct of orderly elections, and prosecution of unlawful actions are all state responsibilities, pursuant of any state's role of exercising police power and maintaining law and order, whether part of a wider federation or a unitary state. During the local, state, and federal elections of 1874 and 1876 in the former Confederate States, all levels of government chose not to exercise their police powers to maintain law and order.[1] Some historians have concluded most Reconstruction governments did not have the power to suppress the violence.[citation needed]

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