Elon Musk gave around $75 million to his pro-Donald Trump spending group in the span of three months, federal disclosures showed on Tuesday, underscoring how the billionaire has become crucial to the Republican candidate's efforts to win the Nov. 5 presidential election.

America PAC, which is focused on turning out voters in closely contested states that could decide the election, spent around $72 million of that in the July-September period, according to disclosures filed to the Federal Election Commission.

That is more than any other pro-Trump super PAC focused on turning out voters. The Trump campaign is broadly reliant on outside groups for canvassing voters, meaning the super PAC founded by Musk - the world's richest man - plays an outsized role in the razor-thin election between Trump and Democrat Kamala Harris.

Musk, the CEO of electric car manufacturer Tesla, was the sole donor to the group in that period.

Musk, who has said he has voted for Democratic presidential candidates in the past, has taken a sharp turn to the right this election. He endorsed Trump in July and appeared with him at a rally in Pennsylvania earlier this month.

Musk's donations to America PAC propel him into the exclusive club of Republican mega donors, a list that also includes banking heir Timothy Mellon and casino billionaire Miriam Adelson.

However, Reuters reported earlier this month that Musk has secretly funded a conservative political group for years, well before his public embrace of Trump.

America PAC declined to comment on the Musk donations. Musk did not immediately respond to a request for comment.

America PAC is focused on encouraging Americans who like Trump but don't always vote to cast ballots this cycle, a high-risk, labor-intensive strategy by the Trump campaign.

The group, which started its work later in the election than other PACs, has encountered some problems with hiring and its contractors. Since July, it has fired two major contractors it has hired to knock on doors.

It has also struggled to hire door knockers in several battleground states in part because by the time the PAC became operational many other canvassing groups had already staffed up, a half-dozen sources briefed on the issues told Reuters.

The group had around $4 million left on hand by the end of September, the filings show.

Separate filings earlier on Tuesday showed that Miriam Adelson, the casino magnate, donated $95 million to another pro-Trump super PAC, Preserve America PAC, in the same period.