By RICARDO CASTILLO     It’s hard to understand why Mexican President Andrés Manuel López Obrador (AMLO) reacted viscerally to the two-level downgrading New York-based Fitch Ratings made of the state-owned oil company Petróleos Mexicanos (Pemex) last Tuesday, Jan. 29. In any case, if there is going to be a culprit for the heinous performance of Pemex finances, it is none other than