The growing opposition to Labor secretary nominee Thomas E. Perez and EPA director pick Gina McCarthy is very similar to what’s going on with the intensifying congressional skepticism about the Obama administration’s performance in the Benghazi consulate attack.

Republicans have raised detailed and substantive concerns about how Perez has performed as Justice Department civil rights chief and what McCarthy has been doing as the government’s principal clean air regulator. Along the same lines, they have uncovered a welter of reasons to wonder whether the State Department was on its toes before the Sept. 11 attack in which the American ambassador to Libya and three others died — and whether it’s been on anything close to its best behavior in explaining itself since.

Without doubting for one moment the sincerity of the GOP motives or the intensity of their legitimate oversight concerns in any of those matters, it’s also totally fair to observe the obvious political and policy benefits for them on all three fronts. It’s possible to have genuine concerns about poor government performance and be politically opportunistic at the same time.

That’s happening on the two Cabinet nominees just as much as it’s happening over Benghazi. In the latter case, the palpable concerns about national security are paired with clear interest in making life as touch as possible for Hillary Rodham Clinton. In the case of McCarthy, the Republican objections to her lack of “transparency” and forthrightness have the added benefit of slowing down the environmental regulations they like least.

And in the case of Perez, the GOP’s multi-faceted disapproval of his work at Justice has the added benefit of obscuring the party’s undeniable interest in keeping a pro-union stalwart from taking over federal oversight of labor-management relations.

The ever-more troublesome future of the Perez nomination was the topic of my conversation today on WAMU, the NPR affiliate in Washington. (You can read a summary here or listen to it here.) The station’s listeners are keenly interested in Perez because he was both a suburban county elected official and Maryland’s labor chief before joining the Obama administration two years ago.