A one-time Senate aide turned lobbyist who pleaded guilty to fraud in the wake of the Jack Abramoff scandal has been spearheading former Pennsylvania Sen. Rick Santorum’s presidential campaign in South Carolina in advance of the state’s pivotal Jan. 21 primary.

James Hirni, a one-time K Street operative who in 2008 admitted buying World Series tickets for Congressional aides in exchange for work on legislation favorable to clients, has for months been drumming up support for Santorum in the Palmetto State. His Facebook profile shows photos of Hirni at Santorum events and well wishes from Santorum supporters. Hirni’s Twitter feed has been devoted almost exclusively in recent days to Santorum’s performance at the Iowa caucuses and the upcoming primary in South Carolina.

“Go Rick!” Hirni posted on Jan. 4 along with a picture of Santorum speaking following his second-place finish in Iowa.

“Huge crowd getting ready to cheer for @RickSantorum!” Hirni tweeted just hours before, posting a photograph apparently taken from the stage.

Hirni did not respond to a request to comment for this story.

Santorum spokesman John Brabender said Hirni is not paid by the campaign.

“He’s not officially involved as a paid staffer with the Santorum campaign,” Brabender said of Hirni. “I can tell you affirmatively that he’s not being paid by the campaign.”

The campaign could not, however, rule out the possibility that Hirni is being compensated for his work by one of the outside political consultancies it has hired, which include Brabender Cox, the Macsata-Kornegay Group,Leibsohn & Associates and Koch & Hoos, among others.

Hirni told a South Carolina newspaper in February that he was merely a dedicated volunteer, but the website of the Republican Party in Greenville County, S.C., lists Hirni as Santorum’s local contact in the state. The email address provided is the same format as those used by formal campaign staffers.

“Hello, this is Jim Hirni with the Rick Santorum for President Campaign in South Carolina,” is the message callers get when they reach Hirni’s voicemail.

Santorum has sought to de-emphasize his longtime links to Washington, D.C., and K Street following a strong showing in Iowa that propelled the one-time Senator into the media spotlight. Santorum’s competitors have begun highlighting his involvement in an effort known as the K Street Project, which sought to place Republicans in lobbying shops and trade associations; Santorum’s affinity for earmarks and his post-Hill career as a consultant to groups that include the faith-based Clapham Group and the government affairs firm American Continental Group.

Hirni also has deep ties to the Washington political establishment. After stints on the Hill for Republican lawmakers including Sen. Jeff Sessions (Ala.) and former Sens. Bill Frist (Tenn.) and Tim Hutchinson (Ark.), Hirni joined prominent K Street firms that included Sonnenschein Nath & Rosenthal, Cassidy & Associates and Greenberg Traurig, where he worked with Abramoff. He spent more than a year as an internal Congressional liaison to Walmart before pleading guilty in December 2008 to one count of “honest services” fraud for providing gifts to Congressional staffers. He was sentenced to one day in jail and two years of supervised release.

Also in South Carolina, a pro-Santorum super PAC called the Red, White and Blue Fund has announced plans to spend $190,000 on pro-Santorum TV ads starting this weekend. PAC adviser Stuart Roy said the group has been inundated with calls and emails since Santorum’s near-win at the Iowa caucuses.

“We’ve been in high gear in terms of additional fund raising,” said Roy, a public affairs consultant whose previous posts include communications director for the National Republican Senatorial Committee. The PAC spent more than $500,000 on pro-Santorum ads in Iowa, Roy said. Its chief organizer is Iowa political consultant Nicholas Ryan, who previously worked on Santorum’s presidential campaign.

Eliza Newlin Carney contributed to this report.