After President Vladimir V. Putin of Russia ordered troops to enter two separatist-controlled enclaves in Ukraine, the S&P 500, which often serves as a proxy for the U.S. stock market, also crossed a notable threshold.
On Tuesday, the S&P 500 fell to 4,304.76, down 1.01 percent for the day. That wasn’t much of a loss, but it nonetheless represented a notable milestone. It brought the stock market down 10.3 percent from its most recent peak on Jan. 3.
On Wednesday, the index dropped another 1.84 percent, bringing its losses from the record to 11.9 percent.
In Wall Street jargon, that meant the S&P 500 is in a “correction,” because its losses since Jan. 3 exceeded 10 percent.
That 10 percent definition is entirely arbitrary and the subject of many quibbles, but…