Heading into Monday, the S&P 500 had tumbled 4% over the prior month, but despite those woes, the benchmark U.S. equity index did at least one thing to encourage the bulls: Honor its 200-day moving average.

A streak of nearly two years worth of closes above the 200-day line for the SPDR S&P 500 ETF (NYSEArca: SPY), iShares Core S&P 500 ETF (NYSEArca: IVV) and the Vanguard S&P 500 ETF (NYSEArca: VOO) came to an end Monday when the S&P 500 closed below its 200-day moving average for the first time since Nov. 19, 2012.

In the midst of its worst three-day run in three years, the S&P 500 looks vulnerable to more losses here. Or perhaps it is ready to rally. That is not mixed opinion, but those statements do highlight the mixed outcomes of what the S&P 500 did following other 200-day line violations in recent years. [A Race to S&P 500 ETFs]

“The index twice fell below the level in 2012 only to recover within two weeks. When it happened in 2010 and 2011, stocks needed at least four months to return to prior levels,” reports Joseph Cioli for Bloomberg.

Bloomberg notes that about 57% of S&P 500 members now reside below their 200-day moving averages. For now, the only ETF tracking either the S&P 500, Dow Jones Industrial Average, NASDAQ-100 or Russell 2000 that remains above its 200-day line is the PowerShares QQQ (NasdaqGM: QQQ). The iShares Russell 2000 ETF (NYSEArca: IWM) has lost nearly 10% in the past month, a move that coincides with small-cap ETF falling below its 200-day line. [Small-Cap ETFs are in Trouble]