Elon Musk’s money machine is back.

The super PAC of Mr. Musk, the world’s richest person, began this week to unleash what is expected to be a $100 million-plus war chest to help the Republican Party in the midterms. The group, America PAC, disclosed the first $800,000 of that spending in 15 races in a campaign-finance filing made public on Wednesday evening.

The spending showed that Mr. Musk was back in the Republican fold a year after he had threatened to break with the party and start a third party of his own after sharply criticizing President Trump’s signature domestic policy bill. Among other critiques, he said the measure was “massive, outrageous, pork-filled” and would spike the U.S. budget deficit.

America PAC is planning to execute a ground game for the right, which it also did in 2024. That year, Mr. Musk’s group worked hand in glove with Mr. Trump’s 2024 campaign, knocking on close to 11 million doors with as many as 5,500 canvassers in the field that worked to turn out low-propensity voters. Mr. Trump regularly praised the efforts of Mr. Musk, even extolling him in his election-night victory remarks: “A star is born.”

It is not clear whether Mr. Musk’s midterm effort will reach the same scale. In recent days, America PAC began running Facebook and Google ads focused on voter registration, including some negatively portraying the New York City mayor, Zohran Mamdani, as a radical avatar of where the Democratic Party wants to take the country.

“If you don’t vote in November, socialism could declare victory over America,” reads the Facebook ad.

On Wednesday, the effort came somewhat into focus. The filing showed spending for Republicans in seven marquee Senate races — Texas, Maine, Ohio, New Hampshire, Iowa, Michigan and Alaska — and eight battleground House races. The expenditures were for “printing,” most likely for pieces of direct mail to be sent to voters.