mexico city mexico attorney general raul cervantes say monday present president enrique pena nieto resignation intense political debate brew implementation new autonomous anti-corruption system replace office come days low house congress discuss new initiatives relate attorney general office order delay laws mexico need decide send enrique pena nieto senate irrevocable resignation cervantes tweet opposition lawmakers object allow cervantes become head new prosecutor general office figure serve nine-year term move away current system president nominate attorney general mexico attorney general resign amid debate new top prosecutor