“When it comes to Palin in Iowa, it’s pretty much Peter Singleton,” said Iowa Tea Party Director Ryan Rhodes. “The guy is everywhere.”

Crisscrossing the state in a series of rented cars, the 56-year-old Mr. Singleton has spent the better part of five months visiting obscure county GOP chairmen, befriending tea-party activists, buttonholing lawmakers in the lobby of the state Capitol, and amassing a database of potential Palin supporters. His base camp is the Days Inn in West Des Moines, where he washes his shirts in the sink.

Deepening the mystery: Mr. Singleton swears he has never met Ms. Palin and has no contact with her team. “I’m just a dedicated activist working on my own,” he said.