Don’t know if its a fact, but someone posted here that S.O.S. cannot be at same location a POTUS as per constitution, continuity, etc.
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I think there’s an issue of whether, while SOS, she can engage in “clearly” partisan political activity such as the convention.
Per the Hatch Act 1939 http://www.osc.gov/haFederalFurtherRestricted.htm
Billary can be as partisan as she wants.