The U.S. stock market has come a long way in a short time. The S&P 500 index closed at a record high Tuesday, nearly six months after coronavirus lockdowns that shut down much of the economy sent the markets plunging. … After plummeting 34% from its Feb. 19 peak, the S&P 500 has staged a steady recovery — gaining more than 50% from its low on March 23. On Tuesday, the S&P 500 finished at 3,389.78 — an all-time closing high.