PITTSBURGH — This city’s last GOP mayor served during the Depression and Democrats outnumber Republicans 5-to-1, but business executive Mark DeSantis has emerged as a serious challenger to Democratic incumbent Luke Ravenstahl, in part because of the young mayor’s missteps.

DeSantis grew up in Sharpsville and graduated from then-Kennedy Christian High School in 1977.

A Republican who won the mayoral nomination as a write-in, DeSantis has government experience, is wooing black voters — despite their history of overwhelmingly rejecting GOP candidates — and is benefiting from a unique set of circumstances.

Ravenstahl is only 27 and was not elected to office. As City Council president, he was next in line to take over when then-Mayor Bob O’Connor died of brain cancer last September.

Ravenstahl landed feel-good spots on David Letterman’s “Late Show” and other national media outlets as the youngest mayor of a major U.S. city, but since then he’s stumbled — several times.

Most recently, Ravenstahl was criticized for using a special police SUV bought with federal Homeland Security funds to take his wife and friends to a Toby Keith concert. Ravenstahl said he did not know how the vehicle was purchased, and stopped using it when he found out.

“The fact that he went from ‘Golden Boy’ to Pinocchio, that is his biggest problem,” said Joseph Sabino Mistick, a law professor and longtime political insider who served as top aide to former Mayor Sophie Masloff in the late 1980s.

DeSantis, 48, runs a high-tech firm, is a former aide to the late U.S. Sen. John Heinz and was a science policy adviser to the first President Bush and later did similar work in the U.S. Department of Commerce.

The first mayoral debate Tuesday attracted a standing-room-only crowd, a sign the GOP has put forward a serious candidate and not just its traditional sacrificial lamb.

“The turnout and enthusiasm established this as a real race,” the Pittsburgh Post-Gazette editorialized, “where perhaps anything can happen.”

Unlike many Republicans before him, DeSantis is actually spending a significant amount on ads, including a daring TV spot that compares him to the city’s most famous ex-mayors, David L. Lawrence and Richard Caliguiri (both Democrats, by the way).

Still, no one is betting that DeSantis will necessarily take more than the 25 percent to 35 percent of the vote that Republican mayoral candidates typically manage in Pittsburgh.

“If all the stars aligned, there could be the making of an upset here, but it’s against the course of history and against odds,” Mistick said. “You just need a young mayor to keep making mistakes. The right one could be a deal breaker.”

Ravenstahl declined to be interviewed for this story, but he has said most of the criticism directed against him has been because of his age, not because of anything substantial.

DeSantis said it’s imperative to erase the city’s $1.1 billion debt and right-size a city government that, despite cuts in recent years, still appears to be shrinking more slowly than the city it serves. Since 1950, Pittsburgh has lost more than half its population, from 677,000 to about 312,000.