U.S. stocks swung to a loss on Tuesday after seesawing rapidly between positive and negative territory. The news came a day after the Dow and S&P 500 posted their biggest one-day declines in more than six years. Stocks overseas extended the rout as well. Some strategists view the losses as a healthy pullback, after a rapid run-up over the last year. They think the improving economic outlook is a positive for stocks overall. Commodities remained gloomy as well.