Tesla’s Troubles Raise Questions About Its Invincibility

Elon Musk appeared to be in a defiant mood Wednesday when he stood before employees at Tesla’s factory near Berlin a week after an arsonist set fire to a high-voltage power pylon and brought production to a standstill.

“They can’t stop us,” Mr. Musk, the company’s chief executive, told workers in a giant tent beside the plant.

But there are proliferating signs that Tesla may not be as unstoppable as it once seemed. The company’s car sales are no longer growing at a torrid pace. Chinese automakers and established brands like BMW and Volkswagen are flooding the market with electric cars. And Tesla has been slow to respond with new models.

Mr. Musk’s many outside ventures, and his penchant for making polarizing political statements and attacking people he disagrees with, have raised questions about how focused he remains on managing Tesla. Wall Street is increasingly concerned about the company: Tesla’s share price has lost one-third of its value this year even as major stock indexes have hit record highs.

“A bet on Tesla has always been a bet on Mr. Musk,” said Eric Talley, a professor at Columbia Law School who focuses on corporate law, governance and finance.

In an interview with the former television anchor Don Lemon that streamed online on Monday, Mr. Musk brushed off the drop in the company’s share price as part of the cycle.