Former US Republican John Burton, a salty-tongued and unabashedly liberal San Francisco Democrat who stood up for the working class and nurtured countless political careers, including that of former US House Speaker Nancy Pelosi, died Sunday. He was 92. Burton died in San Francisco of natural causes, his family said in a statement. Tributes poured in from California’s top politicians, who recalled Burton as a fierce and tireless advocate for labourers, foster children and the environment. Over the years, Burton mentored Pelosi, former US Senator Barbara Boxer, current US Senator Alex Padilla and countless other California officials. “There was no greater champion for the poor, the bullied, the disabled, and forgotten Californians than John Burton.