Mexico’s Attorney General Arturo Chavez stepped down this week after just a year and a half in office. Most media reports cite his poor performance as the reason for his departure. InSight takes a look at the political calculations behind the move, as well as the struggle faced by his successor in gaining approval for her nomination.

Due to the ambiguous nature of the resignation, (Chavez himself has insisted that his resignation was due to “personal matters that could not be put off”) the Mexican media has been buzzing with speculation about the reasons behind it.

El Universal focused on Chavez’s own ineptitude, citing several instances where the former official failed to work effectively with other government agencies like the Federal Investigations Agency (Agencia Federal de Investigacion – AFI).

Still, others in the country believe that Chavez was fired due to pressure from United States authorities. Leonardo Curzio, a researcher at the Center for Research on North America (CISAN), told El Universal that Chavez likely took the fall after it was revealed that the main suspect in the murder case of the U.S. ICE agent last month was released after initially being jailed in 2009 because the Attorney General’s Office did not file proper charges in the case.

A series of U.S. diplomatic memos recently released by WikiLeaks, which highlight American ambivalence towards the former attorney general, may lend some weight to these claims. As the Associated Press notes, several cables written by American Embassy officials in the fall of 2009 call Chavez Chavez’s initial nomination into question, with one —sent from the recently-departed Ambassador Carlos Pascual— going so far as to call it “totally unexpected and politically inexplicable.” In a later cable, another State Department official voices disappointment in Chavez, calling him a “a less capable political operator” than his successor.

Despite the evidence of American disapproval against Pascual, the final strike against Chavez likely came from domestic politics. When he was called to testify to the Mexican Congress about his knowledge of a U.S. federal operation that allowed American arms stores to sell guns to known criminals in order to trace them, Chavez repeatedly avoided doing so. Although he released a statement denying government knowledge of the program, his repeated refusal to testify led to speculation that he was hiding information.

After accepting Chavez’s resignation, President Felipe Calderon nominated Marisela Morales, head of the much-lauded organized crime unit of the federal prosecutor’s office. While she still awaits confirmation by the Mexican Senate, Marisela Morales already has one vote — that of their U.S. counterparts. According to Mexico’s La Vanguardia, Morales was included on a short list of ideal replacements suggested by American officials, and has expressed deep respect for the United States’ role in assisting Mexico’s drug war.

Though it is too early to tell, this endorsement may work against her during the Senate hearing process. As evidenced by the recent outcry against secret U.S. drone flights in the country, Mexicans largely disapprove of perceived foreign military intervention in their territory. If Morales voices too much support for American anti-drug efforts, she could risk losing public opinion in this strongly nationalistic country.