I don't know if you saw the statement the Church issued on the subject, but here it is:
“The choir’s participation continues its long tradition of performing for U.S. presidents of both parties at inaugurations and in other settings, and is not an implied support of party affiliations or politics. It is a demonstration of our support for freedom, civility and the peaceful transition of power.”
I suspect that whichever candidate had won the election, had he/she asked the Choir to perform, the invitation would have been accepted. I definitely don't think the Choir's acceptance of the invitation means, "We love you, Donald! Almost as much as you love yourself!" I was personally very, very disappointed that Trump won, whereas I would have only been very disappointed had Clinton won. I can't stand either of them, but I love good music.