The impasse over the government shutdown and raising the country's borrowing limit showed no signs of breaking Tuesday.
House Republicans have insisted that any temporary funding bill contain concessions on President Barack Obama's health care law.
The Standard & Poors 500 index fell 12 points, or 0.8 per cent, to 1,663 as of noon Tuesday. It's headed for its 11th loss out of the last 14 days.
The Dow Jones industrial average was down 83 points, or 0.6 per cent, at 14,853.
The Nasdaq composite fell 57 points, or 1.5 per cent, to 3,712.