Democratic billionaire J.B. Pritzker has made a $25 million contribution to his campaign for Illinois governor.
The donation means Pritzker has now put more than $100 million of his own money into his bid to unseat Republican Gov. Bruce Rauner.
Rauner, a wealthy former private equity investor, has raised more than $76 million — much from his own bank accounts.
The contest could become the most expensive governor's race in U.S. history, exceeding the roughly $280 million spent in the 2010 California governor's race between former Gov. Jerry Brown and ex-Hewlett Packard CEO Meg Whitman.
Pritzker, an entrepreneur and heir to the Hyatt hotel fortune, also has been giving millions to other Democratic candidates through an effort called "Project Blue Wave."
Rauner has similarly bankrolled GOP candidates.
