Finally, the renewed tariff talk happens even as stocks' valuation has gotten a little over its skis. The S&P 500's forward price-to-earnings ratio is 22.2. Historically, forward returns for stocks are harder to come by when the P/E ratio gets north of 20.

U.S. stocks are lower on Monday after a three-day holiday break as investors keep an eye out for more trade-related developments.

Futures on Wall Street are trading with losses at the culmination of the long Independence Day weekend ahead of US President Donald Trump's looming reciprocal tariff deadline. The Dow futures are currently trading 170 points lower,