US STOCKS-S&P 500 Ends See-Saw Session Lower as Pelosi Visits Taiwan

* Speaker Nancy Pelosi visits Taipei

* Caterpillar falls after missing sales estimates

* Uber surges after reporting positive cash flow

The S&P 500 ended lower after a choppy session on Tuesday, with geopolitical tensions flaring after U.S. House of Representatives Speaker Nancy Pelosi visited Taiwan.

Pelosi said her trip demonstrated American solidarity with the Chinese-claimed self-ruled island, but China condemned that first such visit in 25 years as a threat to peace and stability.

Heavy hitters Microsoft and Visa weighed on the S&P 500, and all 11 S&P 500 sector indexes lost ground, led lower by real estate .

Shares of chipmakers heavily exposed to China were mixed. Advanced Micro Devices rallied ahead of its quarterly report after the bell.

Industrial bellwether Caterpillar tumbled after warning of a bigger drop in demand for its excavators in property crisis-hit China, piling more pain on the industrial bellwether grappling with supply-chain disruptions.

Financial markets have been roiled in recent months by the Ukraine war, soaring inflation and tightening financial conditions.

U.S. job openings in June fell by the most in just over two years, as demand for workers eased in the retail and wholesale trade industries. Overall the labor market remained tight.

After the U.S. Federal Reserve raised interest rates by 75 basis points in July, investors are speculating about whether the central bank's largest hikes are behind it.

"The market has to get really comfortable that they have fully baked in all the Fed's rate hikes, and I think that remains an open question," said Rob Haworth, senior investment strategist at U.S. Bank Wealth Management in Seattle. "The challenges and supply constraints aren't necessarily done. They aren't done and gone yet."

Shares of U.S. defense companies Raytheon Technologies Corp, Lockheed Martin Corp, Northrop Grumman Corp and L3Harris Technologies Inc rallied for much of the session. The United States is Taiwan's main supporter and arms supplier.

According to preliminary data, the S&P 500 lost 26.78 points, or 0.65%, to end at 4,091.85 points, while the Nasdaq Composite lost 19.48 points, or 0.16%, to 12,349.49. The Dow Jones Industrial Average fell 397.29 points, or 1.21%, to 32,401.11.

The CBOE volatility index , also known as Wall Street's fear gauge, eased from the day's high of 24.68 points.

A largely upbeat second-quarter reporting season has supported markets recently, with the benchmark S&P 500 index up about 12% from lows hit in mid-June.

Uber Technologies Inc jumped after the ride-hailing firm reported positive quarterly cash flow for the first time ever and forecast upbeat third-quarter operating profit.

Tesla Inc gained after Citigroup hiked its price target on the electric car maker's stock.

Pinterest Inc surged after activist investor Elliott Investment Management became the largest shareholder of the digital pin-board firm.