The assumption that "only a sitting senator" could get confirmed as Attorney General speaks volumes about the people in the Senate. Jeff Sessions was confirmed with a 52-47 vote. I could be wrong (and we will never know), but I doubt that someone with as troubled a history as Sessions, including being rejected as federal judge because of suspected racism and a damning letter from Martin Luther King's widow, would have survived a confirmation vote. But Sessions was a senator. I don't think he was even particularly well-liked among the GOP caucus, but he was in their club so, senators voted for him who I do not think would have if he was not "one of them."