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There are two plausible explanations for William Barr’s surprising criticism of President Trump yesterday.

The first is the literal one. Barr, the attorney general, lashed out at Trump — for “a constant background commentary that undercuts” the Justice Department — because Barr is legitimately upset. He’s upset not only about the perception that Trump is inappropriately interfering in investigations but also the reality of it.

The second explanation is the performative one. Barr criticized Trump, perhaps even with Trump’s approval, to shore up the Justice Department’s credibility as an independent agency that makes decisions based on the law, not the president’s whims. In this scenario, Barr is happy to use the Justice Department to help Trump but would prefer the help to be less obvious.