The Dow Jones Industrial Average on Monday briefly traded below an important trend line in early Monday trade, underscoring a steady deterioration of the benchmark’s bullish trajectory. The Dow , which was currently paring its losses, traded at an intraday low at 21,600, which puts the equity gauge below its 50-day moving average of 21,629.16, according to FactSet data. It’s the first time Dow has slipped below that short-term average level since mid May. Market technicians consider short-term and long-term moving averages in an asset as a dividing line between downward and upward momentum. The S&P 500 index also is trading below its 50-day mark, which it most recently breached on Aug. 11. The Dow, S&P 500 and Nasdaq Composite Index have been carving out a steady retreat in recent action. All three have ended lower in the past two straight sessions, with Monday threatening to make it a third. On the day, equity indexes were paring losses somewhat, with the S&P 500 trading flat at 2,427, the Dow steady at 21,679, and the Nasdaq looking at a decline of 0.1% at 6,209.