Keeping BYD out won't help if all the other car makers also catch up. If BYD pulls far enough ahead they could just create a US division and make cars here like Toyota and Nissan do. Nissan is on the ropes, so maybe BYD could just buy them and make that their US brand and get all their factories and supply chains.
If Tesla kept iterating on the Model 3, released the Model E, and Musk stayed out of divisive politics that alienate customers, Tesla had a chance to own the mainstream of the US auto market for the next 50 years. I'd say that's gone now.
That's certainly not a thing that's ever happened before. /s
Success is dangerous.
But even the smartest people still get it wrong on occasion.