US stocks are being propped up by AI spending in a way that looks increasingly like a bubble, and that's bad news for anyone holding stocks or bonds when it pops.

• Half of all S&P 500 spending this year is going into AI, with a handful of big tech firms now driving the whole market higher.
• The money is going in circles — Nvidia invests in AI startups, and those startups turn around and buy Nvidia chips, pumping up everyone's earnings.
• Nvidia now wants $500 billion from Wall Street firms like BlackRock and Goldman to keep the boom going, passing most of the risk to regular investors.
• Stocks are more expensive than before the 2008 crash and the dot-com bust, priced as if nothing can go wrong.
• The Iran conflict is still choking oil out of the region, keeping fuel prices and inflation high, which pushes long-term bond yields to their highest since 2007.

Outlook: If AI spending slows or bond yields keep climbing, the whole setup could unravel fast and hit both stock and debt investors hard.