Elon Musk took a surprise trip to China over the weekend.
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- Tesla's stock is a "tech-bubble casino play," J. Bradford DeLong wrote for Project Syndicate.
- The economist thinks the firm no longer keeps up with what CEO Elon Musk promises.
- Musk really wants Tesla to be a tech company, but it's an automaker, DeLong said.
Tesla's market success relies on CEO Elon Musk's ability to keep promising, irrelevant of what the company actually delivers, UC Berkeley economist J.