Wal-Mart fell $1.10, or 1.5 percent, to $74.65, taking the rest of the market with it.
The Standard & Poor's 500 index fell five points, or 0.3 percent, to 1,692.77. Its five-day losing streak is the longest this year.
The Nasdaq composite lost seven points, or 0.2 percent, to 3,761.10.
Worries about the economy and the growing possibility of a government shutdown also continue to weigh on investors' minds. In just a week, the mood of investors has shifted from giddiness over more Federal Reserve stimulus to concern that a government shutdown could harm the fragile U.S. economic recovery.
Two financial deadlines for the U.S. government loom. Congress needs to pass a funding bill to keep the government operating after Oct. 1, when the Federal government's new fiscal year starts. There is also the issue of the nation's debt ceiling, which needs to be raised before Oct. 17, Treasury Secretary Jacob Lew told Congress in a letter Wednesday.
The Republican-controlled House of Representatives has passed a temporary spending bill and a vote in the Democrat-controlled Senate is expected later this week. However, a conflict between the two parties over funding the Affordable Care Act, also known as "Obamacare," has yet to be resolved. Both chambers of Congress have yet to address the issue of the debt ceiling.
"The action over the last few days has been far more tied to the intractably of Congress and the president than the concerns about what the Federal Reserve is going to do next," said Jack Ablin, chief investment officer at BMO Private Bank, which manages $66 billion in assets.
Ablin said investors have bad memories from August 2011, the last time Congress and President Barack Obama fought over the debt ceiling and the budget, which ultimately led Standard & Poor's to downgrade the credit rating of the U.S.
Although the U.S. and Europe are in better shape two years later, there are concerns about real damage to the economy if the budget battle turns ugly. U.S. economic growth slowed considerably in the third quarter of 2011, the same quarter as the downgrade. The slowdown was caused partly by a drop in non-defense-related spending.
The Dow went through nearly three weeks of triple-digit gains and losses during that month, a rough ride that made even hardened Wall Street traders nauseous.
"All we're doing now is worrying," Ablin said.
Wall Street is also looking to next Friday, Oct. 4, when investors get the September jobs report. If hiring is strong enough, the Federal Reserve could decide to start pulling back on its economic stimulus at a two-day policy meeting later in the month.
At the end of its last meeting on Sept. 18, traders had expected a small cut in the Fed's $85 billion monthly bond purchases, which are aimed at keeping long-term interest rates low to encourage borrowing. When the Fed kept its bond-buying intact, the Dow and S&P 500 index soared to all-time highs. Wall Street celebrated that the central bank would keep borrowing rates as low as possible.
But the Fed's decision also left traders worried that the economy wasn't healthy enough to grow without the Fed's help.