Tesla shares surpass $1 trillion in value.

When Tesla was founded in 2003, and for many years after, the chances that sales of electric cars would take off seemed slim. Other automakers viewed electric cars primarily as gas savers, but Tesla envisioned using electric power to make fast, exciting and futuristic luxury vehicles. The company also designed its cars to be controlled almost completely by software that it could update and modify the way smartphones’ can. The concept built a zealous following of customers and investors.

But just four years ago, Tesla was mired in production difficulties at its plant in Fremont, Calif., that Mr. Musk, its chief executive, described as “manufacturing hell.”

Even after straightening out its production difficulties, Tesla remained on shaky financial footing, and it had to raise capital on several occasions. Mr. Musk has said that in the spring of 2018, as it was trying to produce its Model 3 compact sedan, Tesla was just weeks away from financial collapse.

But the Model 3 proved a hit, and when Tesla opened a new factory in China in late 2019, the company’s bottom line steadily strengthened. It is building additional factories in Austin, Texas, and near Berlin in Germany.

How much higher Tesla stock can go is open to question. The company’s sales continue to rise, and it is on track to sell close to one million cars this year. But it still faces many challenges, one of which is increased scrutiny of its Autopilot and so-called Full Self-Driving systems.

Autopilot, which uses cameras to steer and brake a car with little help from a driver, sometimes fails to see other vehicles, a flaw that has led to a series of crashes, including some that were fatal. The National Highway Traffic Safety Administration is investigating why Autopilot sometimes fails to see stopped emergency vehicles. It is looking at 12 instances in which Teslas in Autopilot mode crashed into police cruisers or fire trucks with their lights flashing.

On Monday, the National Transportation Safety Board, in a letter to Tesla, chided the company for failing to carry out safety improvements for Autopilot that the agency outlined four years ago.