WASHINGTON - Independent US Senator Bernie Sanders of Vermont on Thursday announced he would seek the 2016 Democratic nomination for president in a bid likely to pressure Hillary Clinton from the left and challenge her on financial issues.Sanders, a self-described socialist and one of the most outspoken liberals in Congress, faces a difficult fight against Clinton, the presumptive party frontrunner."The people at the top are grabbing all the new wealth and income for themselves, and the rest of America is being squeezed and left behind," Sanders said in an email to supporters declaring his candidacy."The middle class in America is at a tipping point. It will not last another generation if we don't boldly change course now," he wrote.Sanders, 73, is an ardent supporter of left-leaning policies such as expanding Social Security and raising the federal minimum wage. Now in his second Senate term and previously a member of the US House of Representatives, he caucuses with Democrats even though he was elected as an independent.He has cultivated a following among some American liberals for campaigns on income inequality and social issues.