KEY POINTS
  • September is notoriously bad for stocks and worse in midterm election years, but this year has a number of other issues that could affect the market even more.
  • Topping the list is the threat of another $200 billion in U.S. tariffs on Chinese goods which could be announced shortly after Labor Day.
  • Other threats include everything from a rising dollar and emerging markets turmoil to Italy's debt issues. Plus a tweak in U.S. tax law could mean higher interest rates at the end of the month.
A grizzly bear and her cub

Stocks enter the typically rocky month of September near historic highs, and this year the odds are even greater than normal that something big could jolt markets.

Statistically, September is the worst month of the year for stocks, and while the is up about 8.5 percent so far this year, strategists say what's ahead this fall could challenge those gains, including the U.S. midterm elections. August is often wobbly too, but this year's 3 percent S&P gain was the best performance for the month in four years.