The S&P 500 has largely erased its post-election gains the past few weeks. As Trump's inauguration nears, investors seem ready to play the market again.

Often, market performance through presidential terms reverts to more reliable relationships with economic trends, but Trump tends to inject volatility and has foreshadowed bold policy shifts. He is the first President since Grover Cleveland in the late 1800s to serve two non-consecutive terms and his return is being met with a bout of late trepidation in markets.