The S&P 500's (^GSPC) macro moment may be over. As tariff news whipsawed markets to start the second quarter, stocks moved roughly in unison. In April, the one-month correlation of stock movements within the benchmark index soared to nearly 0.7, a level only seen in the past five years when the Federal Reserve began hiking interest rates in 2022 and during the onset of the pandemic. But as President Trump has dialed back the height of his tariffs on other nations, the correlation between stocks in the S&P 500 has...