The S&P 500's return since Election Day has fallen to just around 0.5%. If that holds through Inauguration Day on Jan. 20, it will mark the worst performance for the broad index between an election and inauguration since Barack Obama came into the White House in 2009.

So much for a rerun of the 2016 post-election U.S. stock market rally. The S&P 500 index is clinging to a gain of just 0.8% since Election Day on Nov. 5, threatening to erase the “Trump bump” investors attributed to Donald Trump’s victory.