Stocks have plunged in amid fears that tariffs will weigh on economic growth. Yet, there may be a more under-the-radar reason behind the sell-off.

Key Takeaways The S&P 500 is off to its worst start for a presidential term since 2009, when Barack Obama entered the White House in the midst of the global financial crisis.Traditionally defensive sectors have outperformed since Trump's inauguration amid growing concern that tariffs could usher in a period of stagflation.