The war on drug cartels declared by Mr Calderon after his election in 2006 is seen as having led to a surge in drug-related violence.

BBC: Mexico estimates 26,000 missing since 2006

Meanwhile, the man who was declared the winner, conservative Felipe Calderon, says he is the president-elect.

NPR: Obrador Supporters Cry Fraud in Mexican Election

This morning, they've woken up and Felipe Calderon is winning once again, and he probably will be declared the winner.

NPR: Calderon Holds Lead in Mexican Vote Recount

After he was elected president in 2006, the PAN's Felipe Calderon took a page out of his predecessor's playbook and declared war on the cartels.

CNN: The Mexico drug war: Bodies for billions