The Partido Revolucionario Institucional (PRI) is again on the defensive. The post-electoral row over the legitimacy of the victory of the party’s presidential candidate, Enrique Peña Nieto, took a new twist last week when the Partido Acciόn Nacional (PAN) sided with the left-wing coalition Movimiento Progresista (MP) led by Peña Nieto’s defeated rival Andrés Manuel López Obrador to accuse the PRI of using illicit campaign funds. The PAN, it is important to note, is not throwing its weight behind López Obrador’s legal efforts to invalidate the elections. It still recognises Peña Nieto’s victory. But, the PAN’s decision to cooperate with…