Well, there is the Ineligibility Clause in the Constitution (Article I, Section 6, Clause 2). But that only concerns the ineligibility of cross-serving in the legislative and executive/judicial branches, iirc.
There's nothing I can think of in the Constitution that prevents serving under the executive and judicial branches simultaneously. In fact, John Marshall did exactly that (Chief Justice & Sec. of State, iirc).
There's nothing I can think of in the Constitution that prevents serving under the executive and judicial branches simultaneously. In fact, John Marshall did exactly that (Chief Justice & Sec. of State, iirc).