While the is reaching all-time highs on optimism over Donald Trump's economic agenda, some Wall Street strategists are increasingly worried about a widely followed valuation measure that's reached levels that preceded most of the major market crashes of the last 100 years.



"The cyclically adjusted P/E (CAPE), a valuation measure created by economist Robert Shiller now stands over 27 and has been exceeded only in the 1929 mania, the 2000 tech mania and the 2007 housing and stock bubble," Alan Newman wrote in his Stock Market Crosscurrents letter at the end of November.

Newman said even if the market's earnings increase by 10 percent under Trump's policies "we're still dealing with the same picture, overvaluation on a very grand scale."