After nearly three months in exile, Manuel Zelaya, the deposed president of Honduras, made a stealth return to Tegucigalpa on Monday, taking sanctuary in the Brazilian embassy. He is now using this diplomatic sanctuary to demand reinstatement and stir up his supporters in the streets. This is a dangerous moment, and if violence breaks out the U.S. will bear no small part of the blame.

Mr. Zelaya was deposed and deported this summer after he agitated street protests to support a rewrite of the Honduran constitution so he could...