Wall Street gave up gains Friday after President Donald Trump hit Canada with a fresh 35% tariff and promised more across the board. This came just a day after the S&P 500 set a brand new all-time high.

While tariffs are a tangible worry for investors, something far more nefarious (and important) can weigh on the stock market.

Wall Street posted fresh all-time highs this week, fueled by a relentless rally in Nvidia Corp. NVDA, which became the first company in history to surpass a $4 trillion market capitalization, igniting optimism across the tech and AI sectors.

President Donald Trump has threatened to hike the tariff on Canadian goods to 35 percent, putting new pressure on one of America’s closest allies and trading partners. Stocks fell on Wall Street in response,