Day traders love making bets on tweets from U.S. President Donald Trump, but some of the most prominent quantitative strategists from hedge funds and banks are not quite ready to make big, bold trades on his social media musings. The president's active Twitter presence has lifted volatility in financial markets, which is good for day traders who capitalize on price fluctuations in highly liquid markets. Such traders, who have a short-term horizon, have struggled the last few years as market moves have become steadier and more predictable amid a low interest-rate environment. "Trump's tweets are a good opportunity for a...