(CNN) -- Ahead of their meetings in Mexico City this week, President Obama and Mexican President Enrique Peña Nieto hinted that they wanted to put economic ties atop their agenda. But reports that Mexico is restructuring the way it cooperates with American officials on security matters -- in essence restricting communication -- threaten to impose a shadow over the positive economic story the leaders want to tell. The apparent friction highlights the critical security relationship and illustrates the complexities of U.S.-Mexico relations. "We spend so much time on security issues between the United States and Mexico that sometimes I think we forget this is a massive trading partner, responsible for huge amounts of commerce and huge numbers of jobs on both sides of the border," Obama said this week.
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Presidents Obama and Peña Nieto want to focus on economy
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But the security issue always looms large
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Recent news about changes to security cooperation raises concerns
Obama
Obama
Obama
So in the days leading up to @placeholder's arrival in the Mexican capital, the buzz was not about the economy, but whether Mexico was being uncooperative with the United States.
Mexico City
Mexico
Mexico
Mexico
There is a lot to boast of on the economic front, but security will likely remain a key part of how U.S.-@placeholder relations will be judged.
American
U.S.
United States
I think @placeholder ofificals want to give Peña Nieto the benefit of the doubt."
Enrique Peña Nieto
Peña Nieto
I think U.S. ofificals want to give @placeholder the benefit of the doubt."