Paul Waldman at the Post argues that Whitaker and Barr are under such fierce scrutiny now that they can’t obstruct the investigation, however much they want to.

Democrats are trying to do two things simultaneously with this hearing in particular and their broader efforts with regard to the Mueller investigation. The first is to discover whether there has been any improper interference from the White House to limit the probe. The second is to apply enough pressure that even if Whitaker — or the White House, or William Barr — wanted to hinder Mueller, they’d decide that doing so would be too much of a risk.

The truth is that Democrats have probably succeeded in the latter goal, which must be spectacularly frustrating for President Trump…

All evidence suggests that after pushing Sessions out he appointed Whitaker in an acting capacity precisely because Whitaker had been publicly critical of the Mueller investigation. Yet Whitaker was under so much scrutiny on this question from the moment he took that position, he was almost certainly prevented from doing anything significant to impede Mueller. The same is likely to be true of Barr, who despite being critical of the investigation before his appointment now knows that if he really tries to protect Trump, eventually everyone will know and he’ll be disgraced.

If Trump had actually persuaded anyone to obstruct the Mueller probe on his behalf, he wouldn’t be tweeting “Witch hunt!!!” every few days. Those are the desperate cries of a man who wishes his underlings would obstruct justice on his behalf, but isn’t getting what he wants.

Well…I’m not so sure. Trump tweets what he feels like tweeting, just as he says what he feels like saying. He doesn’t have a whole lot of impulse control, and he keeps flying into rages at the shocking way some people persist in not bowing to him.

But I hope Waldman is right about the larger point.