That is a good question, bearpoker. If you believe that a President is a figure inhabiting an office that is to be idolized, certainly, it is a disgrace. If you believe the president is merely the chief magistrate of the Federal Executive Branch, it is an irrelevancy and has little to nothing to do with his governance whether he went or not; it is of no greater concern than if the head of your local DMV went to a Memorial observance of the fallen. A nice gesture, but certainly nothing that affects his or her governance of the Department. From my perspective, I did not personally care when President Obama engaged in acts of outrage and disrespect towards our country that were overblown by right-wing pundits. Certainly not when he was actually pursuing policies that I believed harmed our country's interests. I am not going to get bent out of shape when Donald Trump personally behaves in a flippant or disrespectful manner. I am more concerned with how he governs, just as I was with President Obama.
As a personal aside, when I became an atheist, I found myself becoming far more worshipful of civic institutions and fonts of Earthly power. Perhaps I was unconsciously filling the void left where God and faith inhabited. Now, as I see it, I am becoming more and more ambivalent towards power and institutions, and I understand the distrust that early philosophical Christians and other ascetic sects have towards them. The idolatry of power is dangerous, and I think Donald Trump serves as a valuable object lesson of this. If he wakes us up to the fact that it is virtue rather than power that is worthy of admiration, all the better.
That aside, I would ask you: What do you think the office of the Presidency is for? Is it merely administrative? Or do you believe the office is more numinous?