It's a rough one in US stock markets today:S&P 500 -1.6%Nasdaq Comp -2.3%Russell 2000 2.5%It's also a bit of a headscratcher as there is no obvious trigger for the decline. Let's look at some possible culprits.1) Chip stocksI lean on the AI theme in part because those are some of the biggest loser today. Nvidia is down 4.2% and threatening the lowest close since Oct 23. Other chip names are also struggling and there are questions about the AI trade in general alongside that. Some of the worries around chip spending and depreciation have been percolating for awhile but China is also making some fairly rapid developments in both chips and open source models that have caught the world by surprise. Overnight ,Baidu unveiled AI chips.2) Fed pricingYesterday, the odds of a Fed cut in December were 66% and now they're 50%. That's certainly a reason to sell risk assets but it also begs the question of why Fed pricing suddenly changed? Yes, we had some hawkish speakers today but Hammack has been hawkish for awhile. The WSJ's Timiraos was out with a report about the divided Fed but that was on Tuesday night and the market rallied on Wednesday. That US government shutdown ended but that's surely been priced in since Sunday night.The thing is, I get it. Pricing it at 50% makes sense to me based on what Powell said on Oct 30. That's when the equity selling should have come but now the kicking and screaming is finally starting. It's strange.3) Looking ahead to 2026We are in a very strong seasonal period right now but I increasingly hear talk about 2026 and it's not great. The tariff Supreme Court decision might come early in the year and if they strike down tariffs, that will create a mess as Trump tries fresh ways to impose them, creating more uncertainty. If they endorse them, then it looks like a captured court that will rubber stamp anything and that has its own set of worries. Further out, there are the midterms and that could be a drag. More pressing, there is the sense that at some point in 2026 there has to be a reckoning on AI, even if it's just the usual nerves and market correction. Then the debate is whether you would be better to wait for a 20% pullback in highly-valued tech names before jumping in. That's a worthwhile debate and has some people shifting into more defensive positions.Again, this doesn't really speak to the timing. The reality is that nothing happened today to trigger this kind of risk aversion and -- notably -- you don't really see it hitting other assets aside from crypto. The FX market is certainly stable and oil is up on the day. Given that, I tend to think this dip is bought but with bitcoin slumping again, it's tough to have conviction in that call. This article was written by Adam Button at investinglive.com.