My post on the fact that the equality requirement did not apply to the federal government, which was expanding on Mike Ramsey’s post, has generated some discussion. See these two posts on the Volokh Conspiracy by Will Baude and by Ilya Somin.
One last point. One way that the equality requirement might apply against the federal government is through due process. The Due Process Clause was applied against the federal government in the 5th Amendment in 1791 and against the states in the 14th Amendment in 1868. Thus, if one can find an equality requirement in due process, one might have an equality limit on the federal government.
But the leading articles on due process claim that the 1791 Clause does not impose an equality requirement. Chapman and McConnell in the Yale Law Journal claim that the 5th and 14th Amendments both impose the same requirement and that requirement does not establish a general equality requirement. Ryan Williams, also in the Yale Law Journal, argues that the 14th Amendment may impose an equality requirement, but denies that the requirement exists in the 5th Amendment — and therefore it does not apply against the federal government.