Private security is very limited in what they may legally do,and some cities add more restrictions. While many people assume private security have the same or nearly the same power as police the criminals are fully aware of the limitations.Essentially ,private security has only the arrest power of any citizen and is usually constrained by employer orders to merely observe and report;escorting troublemakers requires the cooperation of the troublemaker.The police are to be called to do actual “hands-on” removal.It is all about lawyers and liability.The private officer can be a court witness,can close doors, can tell troublemakers to desist, and can defend himself or others only as any other citizen might in the same situation.
DEPUTIZED private security or off-duty police officers hired for event security do have the full police powers in nearly all jurisdictions.(and this is also a reason police unions promote hiring off -duty cops at overtine rates for events).
My limited experience with hiring security is off duty sheriff deputies. I would assume Trump would hire off duty police/sheriff deputies and not just security guards.