WASHINGTON (AP) — The meeting between acting Defense Secretary Patrick Shanahan and his Chinese counterpart began with all the hallmarks of a routine staged and scripted session between two uneasy rivals.

First came the posed photo, as the two men shook hands with broad smiles in front of their nations' flags, and then they moved quickly into the hotel conference room, surrounded by staff. There, Shanahan presented Chinese Defense Minister Wei Fenghe with a gift.

But what at first glance looked like a coffee table book was actually 32 pages of photographs and satellite images of North Korean s...