What would make William Barr quit?

What is William Barr's red line?

It's the question flying around the Justice Department and the legal world as the attorney general is locked in a tense standoff with Donald Trump, who is defying Barr’s public plea last week that the president stop his high-profile punditry about pending criminal cases.

Trump has refused to cease his incessant commentary about the ongoing prosecutions of his former aide Michael Flynn and longtime adviser Roger Stone. After discussing both on Tuesday, Trump indulged his hardcore Twitter habit again Wednesday with a series of retweets painting him and his supporters as beleaguered by the so-called deep state. Trump then retweeted video clips directly criticizing Barr for admonishing him to pipe down.

In response, Barr has said ... well ... nothing — at least in public.