With Mexico's presidential election one month away, the leftist candidate is making modest gains while the incumbent party's contender has slipped, polls show. The polls thus far, however, do not alter the front-runner status of Enrique Peña Nieto of the Institutional Revolutionary Party, the PRI, which is attempting to return to presidential power after a loss in 2000 ended its seven-decade rule. Opinion surveys released this week showed Andres Manuel Lopez Obrador, heading a coalition of leftist parties, inching into second place, dislodging Josefina Vazquez Mota of the National Action Party, or PAN, of President Felipe Calderon. The margin between...