Jr. will be signing and selling his new book Monday at a Costco Warehouse in north Scottsdale.

That has some shoppers at the members-only store wondering what Costco is doing, given the company has an explicit policy against politics in stores.

Costco's website posts a clear policy against politics in stores: "We have found that the majority of our members appreciate the fact that our atmosphere is devoid of politics - so we strive to keep it that way."

12 News asked Costco why it would host a book signing by a surrogate for President Donald Trump during a presidential campaign. The e-mailed response from a spokeswoman didn't quite answer the question:

"We understand that each book or author will not be the preference of every member. We monitor sales closely to ensure we have a varied product mix for our members. At Costco, our book space is limited. We exercise discipline with our selection based solely on what our members are buying."