Long-term U.S. Treasury yields have surged, crossing the 4.50% mark for the first time since July, fueled by worries over fiscal sustainability and resurgent inflation. The move has sparked a sell-off in stocks, with the S&P 500 poised to end its winning streak. Experts warn of potential dollar depreciation and ballooning federal budget deficits, raising concerns about the future of U.S. economic dominance.