Importantly, when Barr was attorney general, the chief of the Justice Department’s Criminal Division was a fellow by the name of Robert Mueller — now the special counsel running the investigation of Russia’s interference in the 2016 election, including any Trump-campaign “collusion” therein.

Barr and Mueller had a fine working relationship. That will come in handy because, once Barr is confirmed, Mueller will again be reporting to him. The two men respect each other and know what to expect from each other. Mueller knows that Barr understands that investigations must be insulated from politics. In fact, when the now-lapsed independent-counsel law was in effect, Barr appointed one in 1992 to investigate the Bush administration’s scrutiny of then-candidate Bill Clinton’s passport file.

Still, Mueller also knows Barr will expect prosecutors to grasp that their authority is limited to deciding whether there is sufficient evidence to charge crimes. It is for Congress and the voters, not prosecutors, to go beyond questions of guilt or innocence, to make political assessments of a president’s fitness or judgment. I believe that, where Mueller has real evidence of a crime, Barr will be his strongest prosecutorial ally; and where Mueller lacks evidence, Barr will expect him to close the case the way prosecutors close cases — without fanfare.