Mexico City ? One candidate was gunned down with his son inside his business. Another is missing after assailants torched her home. In some towns near the U.S. border, parties can’t find anyone to run for mayor.

The violence is intensifying fear that Mexico’s drug cartels could control July 4 local elections in 10 states by supporting candidates who cooperate with organized crime and killing or intimidating those who don’t.

Nowhere has the intimidation been worse than in the border state of Tamaulipas, where Mexican soldiers are trying to control an intensifying turf battle between the Gulf cartel and its former ally, the Zetas gang.

Gunmen burst into the farm supplies business of Jose Guajardo Varela on Thursday and killed him and his son, after he ignored warnings to drop his bid for mayor of Valle Hermosa, a town about 30 miles south of Brownsville, Texas.

On Saturday, authorities said former Mexican presidential candidate Diego Fernandez de Cevallos had disappeared, and his abandoned car was found near his ranch in the central state of Queretaro.

It was unclear whether the disappearance had any relation to organized crime. Officials said there were indications of violence but could not say whether the 69-year-old attorney and power broker had been abducted.