Bangladesh, Feb. 3 -- There is something uniquely reckless about waging political war on your own countrys foreign relations while enjoying the protections of anothers. Sajeeb Wazed Joy has been doing exactly that. Sitting comfortably in the United States, the son of Bangladeshs former prime minister has taken to public forums to smear Washington, insult its institutions, and poison a bilateral relationship that-after years of strain-is finally showing signs of repair.

It would be bad enough if this were merely bombast. It is worse because it is strategic vandalism.

Calling the Bangladesh Nationalist Party an “American puppet,” warning darkly of Jamaat-e-Islamis looming takeover, alleging a “pre-determined” elect...