Spencer Platt/Getty Images
The January decline in stocks has bulls on notice as volatility surges and several technical support levels are broken.Ned Davis Research suggests investors monitor momentum to gauge if stocks will recover in a sustainable way."Another round of breadth thrusts would signal the cyclical bull has a new lease on life," NDR said.Sign up here for our daily newsletter, 10 Things Before the Opening Bell.The S&P 500's year-to-date decline of 9% is on pace to be the worst...