The 10.7% rally in the S&P 500 from its June lows is stumbling as it runs into what has historically been the toughest month for the U.S. stock market, sparking nerves among some fund managers of a broad sell-off in September. The S&P has been in a bear market since plummeting early this year as investors priced in the expectation of aggressive Federal Reserve interest rate hikes, but the index has rallied strongly since June, regaining half its losses for the year. But as investors and traders return from summer holidays, some are nervous about a bumpier ride in September, …
