Wall Street's losses mounted for the second straight day Tuesday as momentum slows on worries about rising virus counts and Washington's inability to deliver more aid to the economy.

The S&P 500 fell 0.3% after spending much of the day swinging between small gains and losses. Most of the stocks in the index fell, particularly banks, oil producers and other companies whose profits tend to track the strength of the economy. Those losses outweighed gains in technology stocks and companies that rely on consumer spending. Traders also welcomed news that AMD has agreed to buy fellow chipmaker Xilinx...