By RICARDO CASTILLO     Suddenly – but not unexpectedly – the once-powerful National Education Workers Union (SNTE) leader Elba Esther Gordillo is back on track to regain the presidency of Mexico’s two-million-member-strong union, the largest in all Latin America. During the administration of former Mexican President Enrique Peña Nieto (2012-2018), Gordillo was thrown in the slammer on several charges, including embezzlement