Ciudad Victoria, Mexico ? A common theme haunts today’s state and local elections across Mexico: drugs.

One gubernatorial candidate has been photographed with a powerful kingpin. Another was arrested for allegedly protecting two cartels. A third was assassinated after pledging to bring peace to his violent state.

Many Mexicans are scared to vote, and others wonder why they should bother if the cartels seem to be in charge anyway.

The elections for governors, mayors and local posts in 12 states is the biggest political challenge yet for the government of President Felipe Calderon, who declared war on the cartels in 2006 and deployed thousands of troops and federal police to wrest back territory from drug traffickers.

A low turnout in the most violent states would signal Mexicans believe the drug lords have more control than ever.

And Calderon’s conservative party is facing a resurgence of the Institutional Revolutionary Party, which ruled Mexico for 71 years through a combination of coercion and corruption that critics considered a veiled dictatorship. That party, known as the PRI, is favored to win in most of the 12 states and gain momentum to regain the presidency in 2012, just 12 years after losing it.

That would add uncertainty to the future of Mexico’s drug war, backed by millions of dollars in U.S. aid and marked by an unprecedented increase in the number of drug suspects extradited to the United States for prosecution under Calderon’s National Action Party.

Nowhere has drug violence so shaken campaigning as in the northern state of Tamaulipas, where PRI candidate Rodolfo Torre was assassinated Monday, less than a week before he was forecast to win the race for governor.

Even Calderon said the attack showed drug cartels were trying to sway the elections. He pleaded with Mexicans to vote and show they would not be intimidated. The PRI nominated Torre’s brother Egidio to run in his place.

For many, the attack was a frightening reminder of the growing power of drug traffickers in Tamaulipas, a state of cattle ranchers and oil wells that is both a PRI stronghold and the birthplace of the Gulf cartel.

Cartel henchmen extort restaurants, car dealerships and junkyards. People avoid highways where caravans of armed men travel openly, their luxury SUVs sometimes stamped with the Gulf cartel acronym. Local media stopped reporting on much of the violence after reporters were beaten and threatened — the Torre assassination being a notable exception.

“For a long time, authorities in Tamaulipas have pretended to govern while criminal groups impose their law,” political analyst Alfonso Zarate wrote in the Reforma newspaper.

Torre, a doctor who served as the state’s health secretary, had mostly campaigned on fighting poverty, even as turf wars escalated following a split between the Gulf cartel and the Zetas gang of hit men. Local politicians often avoid discussing drug trafficking, insisting it is the federal government’s responsibility to fight organized crime.

But Sunday, Torre announced that security would be a priority in his government. The next day, armed men ambushed his campaign caravan, killing him and four others, including his assistant and a state legislator.

Dozens of election workers have since quit, some because their homes were damaged by Hurricane Alex but others because they were afraid to show up at polling stations, said Arturo Miniz, a spokesman for the state election institution.

In Quintana Roo, Cancun Mayor Gregorio Sanchez was arrested last month on charges of protecting two cartels, ending his campaign for governor for a leftist party. He has dismissed the charges as politically motivated.

“People start to think that voting is unnecessary,” said Alejandro Ramos, a civil servant in Cancun. “People have long thought that the politicians have ties to organized crime.”