“I made a mistake,” said Ken Crow, president of Tea Party of America. “I assumed there was an open slot and there wasn’t.”

Monday night, Mr. Crow told Washington Wire that Ms. O’Donnell would appear.

Tea Party of America’s cofounder, Charlie Gruschow, said the group withdrew Ms. O’Donnell’s after receiving numerous “emails from a lot of tea party folks that were very disappointed that she would be speaking.”

“We decided not to have her speak,” Mr. Gruschow said. “We felt it was in the best interest of the movement.”