Michael Wallack, an Indianapolis lawyer, said he created the "dump Trump" page April 8 expecting to attract little notice, the Indianapolis Star reported. The release of President Obama's birth certificate and other recent events have brought thousands of people to the page.
Trump has also come under fire for suggesting Obama was an indifferent student who only got into Harvard Law School because of his race.
"Driving the pace car should not be used as a sound board for some terrible businessman to spew his political aspirations, especially with this being the 100th anniversary," said Chris Hughes, an Indianapolis racing fan.
The Indianapolis Motor Speedway announced Trump would be the pace car driver on April 5, at a time when his presidential aspirations were a bit more muted. Spokesman Doug Boles said the organization has heard from Trump fans as well as Trump detractors.