Los Angeles -- The chief of a powerful federation of unions and an ally of Mayor Antonio Villaraigosa resigned Tuesday amid an investigation into fundraising improprieties surrounding his successful City Council campaign three years ago. "As a result of errors in my judgment, I must take these steps to begin to accept full responsibility for the mistakes that I made," Martin Ludlow, chief of the Los Angeles County Federation of Labor, said while announcing his resignation at the union's downtown headquarters. Ludlow, who resigned from the City Council last year to take the labor job, said he was cooperating with...