A bookstore choosing not to stock a book is not censoring it. A bookstore taking a political point of view is not censorship. A bookstore saying to a customer, “no, we don’t carry that book, and by the way, your taste in reading sucks out loud” might be bad business but it isn’t censorship. (That happened to me once, when I tried to purchase Mistral’s Daughter at a snooty bookstore in Chicago.)
The bookstore in question responds that while it doesn’t support Donald Trump, and doesn’t carry Art of the Deal, it would certainly order it or any other book* for any customer who wanted it. Nice, good business, but intellectual-freedom-wise, not necessary. Bookstores aren’t public libraries, where a request for Art of the Deal, The Woman In Black, or any other book* should be answered, cheerfully or at least neutrally, with a copy, a place in the holds queue, or an ILL form.
*Right after saying they would order anything, the bookseller says it won’t order Mein Kampf. So the line is just in a different place in the sand, I guess.