Three-times presidential candidate Cuauhtemoc Cardenas said the opposition Party of the Democratic Revolution (PRD), which finished runner-up in Mexico's last two presidential elections, had lost its moral authority and needed urgent reform. In an open letter published by his office, Cardenas, 80, said the PRD was "on the verge of dissolving, or ending up as a simple political-electoral franchise subordinate to interests alien to those of the bro…