Yeah, Rosenstein, Mueller, aren't political in a sense that "we" may envision they are, whatever way the chips fall, legally, is how they want it to go. They understand they have a higher purpose to serve the US institutions. Like, the press conference I watched Monday, Rosenstein is with Sessions, talking about transnational Mexican organized crime, CJNG, unsealed indictments, while aware, that in another reality, RR is overseeing an investigation into Sessions boss, and sponsor for the AG spot.
They are serving what they see as a higher purpose, the upholding of rule of law. We may disagree, at times, but ultimately their presence is probably more important that anyone else's, in regard to this specific situation. Guys like McCabe and Comey are the same, except they have broke ranks in a conservative sense, because they feel so strongly that he is a threat to that rule of law. Mueller and RR are still in the belly of the beast, so to speak, so they have to serve first.