What originally made trujillo a target for attacks?

When Trujillo quietly stop a transaction with rebel leader Rafael Estrella Urena in return for Trujillo give Estrella to take power, Estrella would allow Trujillo to run for president in new elections. The rebels moved toward Santo Domingo, Vasquez ordered Trujillo to suppress them, after all, feigning neutrally, Trujillo protect his men in barracks, conceding Estrella's rebels to take the capital virtually unopposed.