Typically, U.S. Presidents are wary of claiming stock market performance as a referendum on their success. Most have seemed to understand that taking credit also means accepting blame, and no one would want to make the tortured argument that the positive moves reflect well on their presidency but that the negative moves do not. But Donald Trump has shown no reluctance to make any argument that suits his political purpose of the day, no matter its absurdity, and no matter if he has to contradict the arguments he made last year, or last week. Perhaps he assumes, as most investors seem to, that the risks are minimal because the Federal Reserve will jump in to save the markets if things turn bad. But in binding his performance so closely to the markets he overlooks the possibility that the Fed will be far less charitable to him than it was to Obama.
The Federal Reserve's Quantitative Easing program, which lasted from the end of 2008 to October 2014, was specifically intended to push up asset prices by lowering long-term interest rates and reducing financial risk. This provides a good explanation why the stock market gained nearly 200% from the bottom in March 2009 to October 2014 despite the fact that the U.S. economy persistently performed below expectations during that time.
Many people, myself included, argued that once the stimulus was removed stock prices would have to fall. Two and a half years later that has yet to occur. Although U.S. stocks are no longer rocketing upwards like they were during the QE era (the S&P 500 is up just 19% since the program wound down completely in November 2014), they have yet to experience any type of meaningful correction. Certainly market observers sense danger, but with the Federal Reserve cavalry always ready to ride to the rescue (as they did in January of 2016), markets have been free to drift upward.