The 'single-best leading indicator for stocks' in recent history is predicting doom

Copper has been the "single-best leading indicator for stocks over the past 18 months," according to one research firm.
Sentiment in the copper market suggests prices should be about 7% below where they are currently trading, a Capital Economics analyst wrote. 
Trade-war tensions and the end of the Fed's rate-hike cycle are bad news for stocks, other experts said. 
Visit Markets Insider for more stories.
Copper prices are signaling a stock-market sell-off may be brewing. 
The red