The Dow and the S&P 500 index on Tuesday are on the verge of halting a monthslong streak without a 1% decline. The Dow Jones Industrial Average was off 176 points or 0.9% at 20,722, while the S&P 500 index was down 0.9% at 2,351. The two main stock-market gauges have gone a history-setting 109 trading days, since Oct. 11, without posting a 1% drop, but a sudden late-morning slide is threatening to push the indexes sharply lower. The S&P 500 needs to decline by about 23 points to register its 1% decline, while the Dow would require a fall of more than 200 points for a 1% tumble. The catalyst for Tuesday’s slump wasn’t clear but financial stocks were among the worst decliners with Goldman Sachs Group delivering the biggest blow to the blue-chip Dow gauge and financials weighing heavily on the S&P 500. The broad-market S&P 500’s streak without a 1% down day is the longest since May 18, 1995 and the longest since Sept. 20, 1993, for the Dow, according to Dow Jones data.