The Globe and Mail reports in its Thursday edition that Wall Street suffered its biggest sell-off in a month on Wednesday as U.S. Treasury yields spiked on worries that government debt would swell by trillions of dollars if Congress passes President Donald Trump's proposed tax-cut bill. The Globe's Darcy Keith writes that the slide in U.S. stocks and rise in yields accelerated midway through the trading session after a $16-billion (U.S.) auction of 20-year bonds attracted only soft demand from investors, in what was seen as a test of foreign appetite for U.S. debt. A deteriorating fiscal outlook has captured the market's attention after Moody's on Friday cut the U.S. sovereign credit rating from the top designation of triple-A. Yields on long-term U.S. bonds have been rising steadily since the start of May, driven by U.S. fiscal concerns and worries that Mr. Trump's unpredictable economic policies will not only stoke inflationary pressures but also erode the appeal of U.S. assets. On Wednesday, the yield on benchmark 10-year Treasuries rose 11.5 basis points to 4.597 per cent and hit its highest level since mid-February. The Dow fell 816.80 points, while the S&P/TSX Composite ended down 214.46 points at 25,839.17.