By Marc Ambinder

Herman Cain on Thursday became the first of this years Republican presidential candidates to receive Secret Service protection. Two sources familiar with the decision confirmed to National Journal that the Cain campaign requested the protection and that it was approved by Department of Homeland Security Secretary Janet Napolitano. Campaign spokesman JD Gordon subsequently acknowledged that Cain is now a Secret Service protectee. News of Cains changed security status was first reported by CNN.

The move comes in a week when Cains campaign has had increasing difficulty with crowd control. On Wednesday a local police officer at a Cain event in Florida clothes-lined a National Journal/CBS News reporter as she was trying to film the candidate. Cain spokesman JD Gordon said afterward that the campaign was reviewing our own internal security procedures.

The Secret Service generally begins to make decisions about providing protection to presidential candidates just before the primary season begins but there is plenty of precedent for candidates receiving it earlier. Agents began trailing then-candidate Barack Obama in May 2007.

Jesse Jackson received Secret Service protection a year before the two elections in which he ran for the presidency 1984 and 1988; when the late Sen. Edward Kennedy whose brothers both were assassinated received Secret Service protection in October 1979 as he was gearing up his 1980 challenge to then-President Jimmy Carter.

Candidates can request Secret Service protection as Cain did. But sometimes the agency will impose its services in cases where it has picked up serious threats.

A bipartisan congressional panel signs off on all requests.

Earlier this year in preparation for the 2012 presidential campaign the Secret Service trained 12 details of agents for candidate protection duty.

Lindsey Boerma contributed.