Elon Musk is demonstrating that a business dependent on one man can have a serious downside. The electric carmaker Tesla, once beloved by progressives, has become, for many, a poisoned brand amid Mr. Musk’s turn to the hard right, and its value is falling fast. What is meant to be his great leap into space, the new Starship, has had two successive and spectacular test failures. To use his own flippant term: Mr. Musk’s wunderkind status could be experiencing a “rapid unscheduled disassembly.”

In rebuttal, he could point to a recent achievement: providing the vehicle for the safe return of two astronauts from the International Space Station. The astronauts had been marooned for nine months because of a flawed Boeing crew capsule, adding to a long list of Boeing fiascos.

The contrast between Mr. Musk and Boeing fits into the folklore of pioneering American businesses, in which the determined risk taker supplants a doddering legacy competitor. Superficially, that is true. Mr. Musk’s SpaceX has eclipsed Boeing in aerospace, just as Tesla, at least for a time, outstripped the conventional auto business. Those were singular achievements. As you look deeper, it’s clear that Mr. Musk’s innovative willpower can become, in the public eye, as much a liability as an asset.

That is clear from the test failures of Starship, a giant rocket designed to be fully reusable. Both of them sprayed flaming debris over the Caribbean and disrupted commercial air traffic, garnering fewer headlines than the astronauts’ safe return. Behind Mr. Musk’s casual brushing away of these incidents lies a serious test of his approach to building space vehicles. The objective is to deliver a version of Starship that NASA will use as part of its Artemis program to return astronauts to the moon’s surface. This would require a ship that not only can be launched into orbit; it would also need to be refueled once there. Clearly, the goal date of 2027 is highly unrealistic.

The first stage of the flights, using Super Heavy booster rockets, is not the problem. That has worked, including the recent spectacular recapturing of the expended booster at the launchpad. But failures near the engines that get Starship into orbit are what’s causing the ship to explode in ways that, according to experts, will require extensive (and expensive) redesign.

SpaceX has never been a one-man show. Its success has as much to do with its current president, Gwynne Shotwell, as it has with Mr. Musk. She gathered a brilliant team of engineers and underpinned his imagination and appetite for risk taking with disciplined management while never coming between Mr. Musk and the limelight. Starship, however, has become like a personal shot of testosterone for him, the most audacious expression of his intention to go beyond the moon to Mars. Its challenges have intensified just as he switched his attention to the Department of Government Efficiency.