The market breadth has never been worse:

Only 17% of S&P 500 stocks have outperformed the index month-to-date, the lowest share since at least 1986.

In other words, 435 stocks in the S&P 500 have declined more than the index in December.

Additionally, over the last 2 trading sessions the ratio of stocks that closed higher to stocks that closed lower hit -42.5% and -40.0%, the 3rd and 4th lowest readings this year.

As a result, the S&P 500 equal-weighted index has dropped -6.6% month-to-date, significantly below the S&P 500's decline of -2.1%.

All while 8 out of 11 sectors have fallen by at least 5%.

The rally is not broadening.