• Political risk. Democrats and Republicans are fighting again about the nation's finances. What's the risk? If they fail to pass a funding bill before the new fiscal year starts Oct. 1, a government "shutdown" is possible. And if they don't raise the debt ceiling in coming weeks, the nation could run out of money to pay its bills and default on its debts.
Both scenarios would likely cause market turmoil and hurt the economy.
"The market," Stovall says, "is worried about Congress ... (causing) drama again."
• Old risks return. "There are definitely reasons for the market to suffer a hangover," says Mark Lamkin, chief market strategist at Lamkin Wealth Management.
For example, confusion over the timing and exit strategy of the Fed's complicated bond-buying program could escalate. Comments from St. Louis Fed President James Bullard on Friday that said the taper could start in October gave investors pause. Interest rates could spike again, as well. And the diplomatic solution to the chemical weapons crisis in Syria might not pan out, putting a U.S. military strike back on the table.
• Earnings risk. The third-quarter earnings season is just a few weeks away, and investors, Stovall says, are sure to ask, "Do we have enough earnings growth to justify elevated" stock prices and valuations? Profit growth of 3.8 percent is expected for the September-ending quarter, down from 4.9 percent last quarter. And the 10.1 percent growth in profits expected in the final quarter of 2013 might be too rosy, he adds.
But for now, stocks look good as long as the Bernanke-led Fed keeps pumping cheap money into the economy and markets, Lamkin says.
(Read more: Bulls gone wild: Money flows hit a new record)
—By Adam Shell, USA Today.