Just three months ago, Elon Musk stood before a crowd of roaring conservatives and held up a chain saw. He was at the height of his influence, swaggering in a self-designed role with immense power inside and outside the government.

“We’re trying to get good things done,” he said, using the chain saw as a metaphor for the deep cuts he was making in government. “But also, like, you know, have a good time doing it.”

Mr. Musk’s time in government is over now. His good time ended long before.

Mr. Musk left his government position on Wednesday, after weeks of declining influence and increasing friction with both President Trump and shareholders of his own private companies.

Mr. Musk’s time in Washington has brought significant benefits to his fastest-growing company, SpaceX, the rocket and satellite communications giant. Musk allies were chosen to run NASA and the Air Force — two of SpaceX’s key customers — and one of the company’s major regulators, the Federal Communications Commission.

But Mr. Musk never came close to delivering on the core promise of his tenure: that he could cut $1 trillion from the federal budget.

His Department of Government Efficiency was full of government newcomers who struggled with both the law and the facts. They posted error-filled data and made procedural mistakes undercutting their credibility. They also rushed through cuts without seeming to understand what they were cutting. On the group’s website, 47 percent of the contracts they canceled are listed as saving taxpayers nothing.