Jack Goldsmith:

It's significant for a couple of reasons.

First, it shows that people in the White House, including those closest to the president, thought it would be a disaster for the president — that's the way The New York Times reported it — if he fired Mueller.

And, second, and I think most importantly, it shows how very difficult it would be, in fact, for the president to fire Mueller. If senior aides close to him like Don McGahn are willing to resign to prevent that from happening — and we don't quite know what his motivations are — that suggests that the president is not going to be able to find somebody to carry out, or it's going to be very difficult to carry out any attempt to fire Mueller.

And, moreover, that happened seven months ago. The president has new lawyers since then. He, at least in his public pronouncements, has seemed to have calmed down about Mueller.

One way of looking at it is that there was resistance in the White House of this happening and that it's going be harder for Trump to do this than we might have thought.