The S&P 500 fell 7 percent last week. It's fall since its last high brings it just about 2 percentage points from the 20 percent decline that is considered to be a bear market.
The Nasdaq Composite is already in a bear market, having fallen 22 percent from its high after another 8.4 percent tumble last week.
A CNBC report noted that after trading in a range of 2,600 to 2,800 for four months, the S&P 500 quickly fell out of it all the way to 2,400.
"The next level traders would like to see tested is 2,250 to 2,300," said Scott Redler of T3Live.com.
For the near term, investors could be focused on the partial government shutdown in the US after Congress failed to pass spending bills ahead of the deadline amid disagreement over funding of President Donald Trump's proposed border wall.
Mark Cabana, head of US short rate strategy at Bank of America Merrill Lynch, said that the disagreement is "a signal about just how difficult things will ultimately be".
However, for next year, the key concerns are trade and monetary policy.
"If we moved into 2019 and all tariffs were implemented, that would very quickly outweigh all stimulus we have coming into 2019," Wilmington Trust chief economist Luke Tilley said.
On Friday, the US stock market briefly rallied when New York Fed President John Williams said the Fed is willing to reconsider its policy depending on the economy and conditions.
Still, Cabana said that "rates could be higher" and while the 10-year Treasury yield fell to 2.78 percent on Friday, he thinks a yield of "3 percent is reasonable".