On Thursday, Herman Cain became just the 12th presidential candidate known to have received Secret Service protection during his campaign.

The Secret Service confirmed that Secretary of Homeland Security Janet Napolitano had authorized protection for Cain at the request of the Cain campaign and after consultation with a congressional advisory committee.

Ed Donovan, a spokesman for the Secret Service, told Politico that it was not that unusual for a presidential candidate to receive official protection, even a year before the general election. He said that several prominent or controversial figures, including Jesse Jackson, Edward Kennedy, Pat Robertson and President Obama, have received early protection as candidates.

But while there is clearly precedent for the practice, it is very rare in the context of the large number of candidates who run in each election. Cain is the only 2012 candidate, aside from Obama, whom the Secret Service is protecting.

It is not enough just to be a controversial candidate: the Secret Service does not usually protect someone unless there has been a credible threat to their safety. But Donovan refused to say whether the Secret Service was aware of threats against Cain.

We don't discuss the deliberations on which an assessment is made, he said.

Cain, a Georgia businessman who led most national polls last month, has become an increasingly contentious figure since Politico reported that two women had filed sexual harassment complaints against him in the 1990s. Since then, two additional women have come out to accuse Cain of sexual harassment, and his poll numbers have dropped significantly.