Cut the EU off from ... what?

Technlogy? That would likely result in a US market crash the likes of which has never been seen before. Look at what percentage of the stock market is the magnificent 7. Now imagine what would happen to that if US tech giants were no longer allowed to sell their products/services in the EU. The market is fragile as it is with the AI bubble going on.

Trade? That cuts both ways, and the US economy and cost-of-living crisis doesn't give them lots of wriggle room.

Products? China will be all to happy to step into whatever market is thus competition-free, not to mention the impact this would have on US businesses.