The 10% trigger for a correction is an arbitrary, round-number threshold. But it serves as a signal that investors have turned pointedly more pessimistic about the market.

But uncertainty around Trump's tariff policy continues to grip Wall Street, and his trade war has only intensified this week. The president has vowed to respond to tariffs planned by the EU and Canada in response to US duties on steel and aluminum imports — most notably leading off Thursday by threatening a 200% tariff on imports of EU wines and spirits.