 U.S. stocks capped another wobbly day of trading with modest losses Wednesday as Wall Street waited for any signs of progress as lawmakers in Washington negotiate over how to deliver more aid for the economy. The SP 500 slipped 0.2 after shifting between small gains and losses for much of the day. The benchmark index is on track for its first weekly loss after notching gains in each of the past three weeks. Losses in industrial stocks, health care companies and elsewhere in the market outweighed solid gains by communication services stocks. Treasury yields were mixed. Much of Wall Streets focus has been on Washington, where White House officials and Democrats are negotiating on another round of support to prop up the still-struggling economy, though the prospects for a deal that delivers aid soon remain cloudy. As long as the parties involved give the market a headline suggesting theyre still negotiating, theres a kernel of optimism in the market, said Quincy Krosby, chief market strategist at Prudential Financial. But then theres also concern that this is extreme political posturing and that a deal will not be forthcoming. The SP 500 fell 7.56 points to 3,435.56. The Dow Jones Industrial Average lost 97.97 points, or 0.4, to 28,210.82. The index had briefly been up 141 points. The Nasdaq composite gave up 31.80 points, or 0.3, to 11,484.69. Stocks of social media companies were among the biggest gainers after Snap reported even bigger jumps in revenue and in the number of Snapchatters using its service each day than analysts expected. Snap surged 28.3 following its quarterly profit report. In its wake, Twitter jumped 8.4, the biggest gainer in the SP 500, and Facebook rose 4.2. Googles parent company rose 2.3, adding... 