Question: The failed Escobar Rebellion of 1929 challenged the political power of what political leader, who had been the interior minister under Mexican President Alvaro Obregon?  
Sentence (from "Plutarco Elías Calles"): Calles indeed tried to fulfill his promises during his populist phase (1924–26), but entered an anti-clerical phase (1926–28).
Relevant evidence: No