S&P 500 losing streak runs to 8 days as Facebook weighs

Facebook shares tumbled 5.7 percent as the world's largest online social media network warned that revenue growth would slow this quarter. The stock was the biggest drag on the S&P 500 as well as on the tech-heavy Nasdaq, which also posted its eighth straight day of losses. Investors have been unnerved by signs the U.S. presidential race between Democrat Hillary Clinton and Republican Donald Trump is tightening, after Clinton had until recently been thought to have a clear lead.