(CNN) - Mark Sanford's besieged congressional campaign is being outspent almost 3-1 on the television airwaves by his Democratic foes, a media-buying source tracking the South Carolina House campaign told CNN.
Democratic candidate Elizabeth Colbert Busch and allied groups have spent well over half a million dollars to date on broadcast and cable ads in the Charleston and Savannah media markets, which blanket South Carolina's First Congressional District.
Sanford and the South Carolina Republican Party have spent just a fraction of that total on television spots, the media-buying source said. No outside GOP organizations or conservative groups have booked airtime in the district.
Colbert Busch's campaign, which began running TV ads before Sanford captured the GOP nomination, has been the biggest spender among the Democratic groups playing in the special election.
She has been aided by the Democratic Congressional Campaign Committee in Washington, which will go up with a negative ad against Sanford on Friday and has booked TV time through next week.
A Democratic outside group, the House Majority PAC, also started to pump money into the race this week and is expected to stay on air through the May 7 election.
The stark disparity should come as no surprise to those following the race closely.
The National Republican Congressional Committee told reporters Wednesday that they will not commit financial resources to the race in the wake of news that Sanford has been accused by his ex-wife of repeatedly trespassing on her property.
Sanford attempted Thursday to turn the spending disparity into an advantage by tying Colbert Busch to "Nancy Pelosi and national Democrats."
"My opponent has gone through great lengths to distance herself from the liberal Beltway crowd, but it simply isn't believable that those same folks would be trying to buy this race for someone who would truly be an independent voice in Washington," Sanford said in a statement released by his campaign.