In terms of Bercow's remain vote, I don't see that as breaching impartiality. He obviously will have his own views on many (all) matters and I can't see that it's a problem if we know what the are. If there is no clear evidence of bias in his refereeing of Brexit debates, that's the end of the matter in my book. But the Trump speech was different. An invitation to speak is in the gift of the speakers and the Lord Chamberlain, but I've always understood, and all I've read supports the view, that the speakers are meant to ensure they are reflecting the views of their respective houses before they make decisions of that sort.