One of Mexico’s six presidential candidates formally withdrew from the race yesterday, throwing his support behind the leading opposition candidate. The move by Porfirio Muñoz Ledo came as the campaign continued to heat up ahead of the July 2 election, with opposition candidates accusing the party that has governed for 71 years of pressuring voters. Most polls show Vicente Fox of the opposition National Action Party, known as the PAN, and Francisco Labastida of the ruling PRI in one of the tightest races in Mexican history.