Joining what some are calling the nation's largest mobilization of immigrants ever, hundreds of thousands of people boisterously marched in downtown Los Angeles Saturday to protest federal legislation that would crack down on undocumented immigrants, penalize those who help them and build a security wall on the U.S. southern border. Spirited crowds representing labor, religious groups, civil-rights advocates and ordinary immigrants stretched over 26 blocks of downtown Los Angeles from Adams Blvd. along Spring Street and Broadway to City Hall, tooting kazoos, waving American flags and chanting "Si se puede!" (Yes we can!). The crowd, estimated by police at more...