Mr. Musk dug into his companies’ budgets, preferring to cut too much rather than too little and to deal with the fallout later. Under Donald Trump, he is set to apply those tactics to the U.S. government.

Over the last 16 years, Musk's business deals with the government total nearly $20 billion, according to federal contracting data.

On a Saturday morning in December 2022, Elon Musk summoned finance executives at Twitter, which he had bought six weeks earlier, to a conference call. Then he drilled into a spreadsheet that contained the social media company’s expenditures.