One reads various places including occasionally on B&B that one should not wear a button down shirt with a suit, unless one is going for some kind of informality. I have always countered that a button down shirt is considered entirely proper and serious in top corporate and government circles--that all one has to do is look at formal photos of CEOs and government officials. In this vein, I could not help but notice that Robert Mueller invariably wears a white button down shirt with a conservative suit, including for his recent testimony before Congress. Similarly, I notice that Attorney General William Barr nearly as often wears a button down shirt including for official government speeches. One could say this style of dress derives from the Ivy League. Mueller did go to Princeton undergrad and Barr to Columbia. Mueller went to the University of Virginia for law school, which might as well be Ivy League as far as style of attire goes.