His point is that foreign states could blackmail you or exert pressure in other ways, even if they aren't gonna extradite and throw you in jail following due process. Thus, Russia/China would have "coercible locals" in western countries.
In the US a "coercible local" is given a far less scary descriptor of confidential informant, or state's evidence. There are far more of those than there are "coerced locals" in the service of Russia or China.
