In the closing years of the cold war, as relations between the Soviet Union and US thawed, Ronald Reagan adopted a Russian proverb: trust, but verify. These days, with Sino-US relations chilling rather than warming, there is precious little trust, and limited ability to read the other’s intentions accurately. Relations were deteriorating long before the Chinese balloon floated into US airspace and the military shot it down. Everyone knows that the US spies on China and vice versa; it is also obvious, despite Beijing’s feigned outrage, that it would take swift action against a US device appearing in its skies....