The S&P 500 has jumped 42% under President Trump — according to market data from the inauguration through 2019's final day of trading.

Why it matters: Trump uses the stock market's surge as a barometer of his presidency's success — one that, along with the 50-year low unemployment rate, he's sure to continue to tout as the 2020 election approaches — but the gains under him lag those under former Presidents Barack Obama, when stocks rebounded from the lows of the financial crisis, and George H.W. Bush.

Even if you count the 2016 post-election day market rally, the S&P's performance is still behind former President George H.W. Bush (measuring from election day through the end of the third year in office).

The bottom line: Only about half of Americans own stocks, "largely through retirement accounts," as the Washington Post notes, citing Federal Reserve data.

Meanwhile, Trump's trade war, which added to stock market volatility, has cut into the financial well-being of America's farmers.

Go deeper: