Steve Pajcic, a lawyer and philanthropist in Florida, started a group that is airing ads in Kansas and South Carolina. Florida and Mississippi are next.
The campaign is set to be more expensive than the 2024 presidential election cycle, and has already exceeded the ad total booked by the N.F.L. last season.
The world’s richest person has quietly become by far the biggest known midterm donor, trying to save Republicans’ Senate majority with some of the largest donations in American political history.
Elon Musk has shown less public interest in elections in recent months, but he has patched up his relationship with President Trump and quietly spent enormous amounts to help Republicans in the midterms.