It’s rare for the S&P 500 and the VIX to post gains on the same day. Here’s why it just happened.

The S&P 500 and VIX rose in tandem Tuesday. - MarketWatch photo illustration/iStockphoto The stock market has been climbing despite rising geopolitical tensions after the U.S. captured Venezuelan leader Nicolás Maduro. In the wake of the weekend operation, the S&P 500 index SPX gained 0.6% on Monday and another 0.6% on Tuesday. Perhaps more interesting, however, is that as stocks were gaining, investors were positioning themselves for volatility. The Cboe Volatility Index VIX — often referred to as Wall ...