Thiel's $15 million super PAC investments helped boost Ohio's J.D. Vance and Arizona's Blake Masters in their competitive primaries earlier this year, with the California billionaire even influencing former President Donald Trump's decision to endorse both candidates.

But since the two candidates won their respective nominations, Thiel has not stepped up with additional investments as Vance and Masters have struggled to raise money on their own -- while both have been massively outraised by their Democratic rivals.