If Mueller gets called to testify, we should ask him whether the investigation ended entirely on his own terms.

Remember the investigation ended soon after Barr took over. And even though they said Mueller didn't have any specific requests denied, that doesn't mean he didn't obey an order to end the probe.

I actually don't think that Barr shut the investigation down prematurely. But given all his fuckery, we should still just verify this with Mueller.