Some terms come to mind that could describe Vivek and what he is doing on behalf of Pres. Trump:
A Town Crier, is an officer of a royal court or public authority who makes public pronouncements on behalf of the Royalty
An Opening Act, is one who warms up the crowd for the Headliner
A Heralder is one that conveys news or proclaims : announcer, forerunner, precursor, harbinger. One that goes before or announces the coming of another.
A Presage is an person or thing that forewarns of things to come
An Ambassador is one who acts as a representative or promoter of a specified person or cause an accredited diplomat sent as an official representative to a person, cause or country
An Advocate is one who publicly supports or recommends a particular person, cause, or policy
A Messenger is a person employed to convey official dispatches, messages, instructions or updates as dictated by others above him
A Surrogate is a substitute, especially a person deputizing for another in a specific role or office
A Proxy is someone given the power to represent another person
Some terms come to mind that could describe Vivek and what he is doing on behalf of Pres. Trump: