S&P 500 (SPX) bulls face a critical level to hold, argues @CharlesSchwab's Rachel Dashiell. She takes investors through the index's 4-month price action to highlight how weaker market breadth is putting a recent breakout at risk. Rachel then looks into a slice of the S&P through the energy sector, pointing out an "extreme correlation" with the rally in 10-year Treasury yield that she believes has risk of unwinding.