Not authority; credibility. It's a nitpick, but the distinction is important when we're discussing government agents. Credibility is essentially rhetorical authority ("I am willing to take your word because I consider you an expert in the relevant domain"), rather than the kind of authority derived from official bestowment of power.
But we're talking about this guy named Stewart Baker, who just so happens to have authority as a senior officer of the executive branch of the United States Government.
This is also a type of authority. It is not the relevant type of authority when discussing whether or not a statement is an ad hominem.
Not authority; credibility. It's a nitpick, but the distinction is important when we're discussing government agents. Credibility is essentially rhetorical authority ("I am willing to take your word because I consider you an expert in the relevant domain"), rather than the kind of authority derived from official bestowment of power.