The top 40 donors gave $2.4bn up until 14 October, according to the liberal-leaning think tank Brennan Center for Justice, external, which is a record high for that point in a midterms cycle.

"Spending in the 2026 midterms is shattering records, with more of the money coming from the wealthiest donors and groups this election," says Michael Beckel, a US campaign finance expert.

As well as individuals, organisations can also give to Pacs. For example, Geosor Corp and Fund for Policy Reform, both founded by the billionaire financier George Soros, have given a combined $102m to liberal groups.

Aside from Soros, former New York City mayor and businessman Michael Bloomberg has been the biggest Democratic donor, giving more than $60m.

Several billionaires including Jeff Yass, who runs one of the world's largest trading firms, and Richard and Elizabeth Uihlein, the owners of a US business supply company, have given over $100m this campaign to Republican causes, according to FEC filings.

But Musk has given by far the most of any individual, donating almost half a billion dollars as of October.