A bill that the Mexican president is expected to approve soon would curtail private investors in the energy industry and possibly reverse gains in lowering carbon emissions. President Andrés Manuel López Obrador has never been short of criticisms about his predecessor’s legacy. But he has reserved a special contempt for the sweeping overhaul that opened Mexico’s tightly held energy industry to the private sector.He has called the changes a form of legalized “pillaging,” the product of corruption and a resounding failure. He has suggested that some foreign energy investors are “looting” the nation and that Mexican lawyers who work for...