Nafta is a tough nut to crack for López Obrador

While Mexico presses for a successful renegotiation with the United States on Nafta, negotiators have confronted a new challenge in the form of concerns voiced by president-elect Andrés Manuel López Obrador over the 2013 energy reform.

There is a debate among the transition team over the issue of energy within the talks, which are being held in private.

The Nafta energy rules that are now in doubt were negotiated last year and aimed to provide security for investors.