A look at the day ahead in U.S. and global markets from Mike DolanRancorous geopolitics continues to grab most headlines again this week, but it's creeping anxiety about a slowing U.S. economy that's unnerving investors most about Wall Street stocks.Wary of Wednesday's results from megacap chip giant Nvidia (NASDAQ:NVDA), the S&P500 lost its 6,000 handle for the first time in three weeks on Monday and both the tech-heavy Nasdaq and small cap Russell 2000 are now negative for the year to date.Even the meagre 1% gain in the S&P500 for 2025 so far is a third of MSCI all-country and far below the 13% gain in Germany's blue-chip DAX, which was emboldened this week after the election results there and hopes for some fiscal easing.The VIX 'fear index' of S&P500 implied volatility also jumped above 20 for the first time since February 3 and was eyeing up its highest close of the year ahead of today's bell.Adding to the tech angst ahead of Nvidia's update, Chinese mainland and Hong Kong stock indexes both lost more than 1% earlier on Tuesday after a Bloomberg report said President Donald Trump plan to toughen chip restrictions on China - expanding predecessor Joe Biden's efforts to hamper Beijing's tech development.'ON SCHEDULE'Keeping trade threats on the front burner, Trump also said overnight that tariffs on Canadian and Mexican imports are "on time and on schedule" despite both countries' moves on border security and fentanyl trafficking ahead of a March 4 deadline.investing.com