Mexico's then-President Vicente Fox, left, speaks with Felipe Calderon, Mexico's president elect, at the presidential residence Los Pinos in Mexico City, September 21, 2006. Daniel Aguilar/Reuters

Former Mexican President Felipe Calderon left office almost four years ago, but during his six-year term he presided over one of the most violent periods in modern Mexican history.

Taking office in 2006, Calderon initiated a military-backed crackdown on organized crime that led to peaks in violence between 2010 and 2012.

Calderon left office in 2012, and homicide rates have fallen and risen again under his successor, Enrique Peña Nieto.

Calderon, in the eyes of many, is tied to the growth of violence over the last decade, but it doesn't appear he's interested in discussing it.

While taking questions recently in Tamaulipas, a northeastern Mexican state racked by violence, Calderon was asked, "Do you feel some responsibility for the insecurity in Tamaulipas, Mr. President?"

His reply, after a brief pause: "Another question, please."

When Calderon assumed office in December 2006, after narrowly defeating leftist candidate Andres Manuel Lopez Obrador, he "really embraced and sort of projected a more prominent role for the military,” David Shirk, a professor at the University of San Diego and director of the school's Justice in Mexico program, told Business Insider late last year.

Calderon “signaled his intention to give the military a prominent role in domestic security and particularly counter-drug operations,” Shirk said.

Calderon's predecessor, Vicente Fox, had deployed troops to Tamaulipas in 2005, but Calderon soon doubled down on this tactic, making it part of a broader, more forceful strategy to crackdown on organized crime and drug trafficking.

Wearing a military cap and jacket, Mexican President Felipe Calderon, center, walks with state and military officials to meet with federal forces involved in ongoing anticrime operations in Apatzingan, Michoacan, January 3, 2007. Calderon sent 7,000 troops to his home state of Michoacan immediately after taking office on December 1. AP Photo/Guillermo Arias

In 2007, Calderon increased troop deployments throughout Mexico from 20,000 to 50,000 soldiers, shifting troops into urban areas, like Ciudad Juarez and Tijuana, as part of a new focus on drug-trafficking hubs rather than on rural production zones.

Around 2010, the Mexican government was engaged in what has been called the kingpin strategy, targeting the top leaders of these criminal organizations, believing that eliminating the leadership would cause the structure to wither away.

"But what actually happens [with the kingpin strategy] is that if you take out the head of [an] organization ... it creates power vacuums and leads to ... both internal schisms and fighting within the organization ... and encroachment and creation of new spaces for other actors that can come until we see a multiplication effect, or a proliferation of smaller, regional groups," Shirk told Business Insider recently.

These groups compete with each other more violently and wantonly and commit lower-level crimes than larger cartels or organized-crime groups.

In 2010, the Zetas and the Gulf cartel, erstwhile allies, split, sparking a violent conflict that upped the bloodshed and brought about further deployments of Mexican security forces. This conflict drags on today, with internal rifts and new criminal groups adding to the array of combatants competing for influence in Tamaulipas.

Soldiers escort five alleged members of the Zetas drug gang during their presentation to the press in Mexico City, June 9, 2011. Alexandre Meneghini/AP

"Their primary objective is to control the seaports and the international bridges into the U.S. It is a lucrative drug route for these criminal groups," Mike Vigil, a former chief of international operations for the US Drug Enforcement Administration, told Business Insider earlier this year.

"The criminal groups in Tamaulipas not only engage in drug trafficking but also kidnapping, extortion, and theft of petroleum," Vigil added. "Currently, the state has one of the highest kidnapping rates in the country."

Homicide cases in Tamaulipas remain well above the numbers seen 10 to 15 years ago. Mexican government data

Accordingly, over the last half-decade Tamaulipas has seen homicide numbers well above what was recorded during Fox's term and the first half of Calderon's time in office.

And while the state saw a decline in homicides at the start of Peña Nieto's term (a trend seen across the country), its homicide levels are still above those of a decade ago.

Mexican security forces took down a number of Zetas leaders between 2012 and 2015, but the effect has been more insecurity, not less.

A split between Zetas factions in Ciudad Victoria, the Tamaulipas state capital, has made things particularly bad there.

"The way of life has changed completely here in Victoria," a small-business owner told Vice, speaking in hushed tones. "It's worse than it's ever been."

Local politicians and state and local police forces have come under the sway of criminal groups, rendering them ineffective, if not complicit, and necessitating further federal intervention.

"It is a known fact that state and municipal forces in Mexico are highly corrupt and the military and federal police refuse to work with them," Vigil said.

Another businessman in Ciudad Victoria told Vice the recent violence was the result of a "power vacuum" created by recent elections for state governor that weakened existing corruption deals and created an opening for outside groups to mount an invasion.

The areas of influence of Sinaloa-based organized-crime groups, shown in light orange, alongside those of Tamaulipas-based organized-crime groups, shown in light green. Stratfor

The businessman said such corruption deals were the only viable approach to Tamaulipas' organized-crime problem. "All of us are hopeful that the new government will have a good arrangement with one of the groups of bad guys," he told Vice, "so that the cartels let us work and let us live."

"Corruption has allowed criminal groups to institutionalize their own rule of law," Vigil added.

For Calderon, his recent questioning about violence in Tamaulipas is not the first time he has been confronted in public about the legacy of his crime-fighting policy.

Late last year, while attending the Mexican Grand Prix in Mexico City, the former president was greeted by shouts of "asesino" — or "murderer" — by spectators.