CHARLESTON, S.C. - The GOP runoff for a state Senate seat in Charleston is heating up with the challenger accusing the incumbent of "negative, gutter politics."

Challenger Chip Campsen, a former aide to Gov. Mark Sanford, went on the offensive Tuesday, holding a news conference to rebut recent remarks by Sen. John Kuhn.

On Monday, Kuhn called his opponent hypocritical because he said Campsen preached reform as a former House member and, Kuhn said, Campsen used political connections for personal gain.

Campsen's family business, Fort Sumter Tours Inc., has a contract with the National Park Service to ferry tourists to and from the site of the beginning of the Civil War.

In 1993, the business Campsen helps manage sued the National Park Service over a franchise fee increase that tripled. Campsen, a former state representative, said park service accountants in Washington had over-calculated the company's income, partly because they added profits from non-Fort Sumter trips, such as nighttime dinner cruises.

Fort Sumter Tours lost several court decisions before Sanford, who was then a congressman, intervened with legislation that forced the park service to "work with" the company. Officials announced in July 2002 the dispute had been settled and the company would pay about half the original fee - $1.12 million to cover extra fees from June 1991 to December 2000.

Kuhn said the events show Campsen used his family and political clout to get a reduction in a debt "which resulted in a taxpayer-funded $1 million financial windfall for his private business."

Campsen said Kuhn is desperate and "an incumbent who knows he's in trouble."

Campsen got the most votes in the June 8 primary but must face Kuhn in a runoff June 22 because neither candidate had more than 50 percent of the vote in the three-way race. Campsen received 42 percent, and Kuhn finished second with 36 percent.

Campsen also was upset Tuesday that a letter he said was sent to voters by Kuhn's campaign attacked his character.

The letter, which has former state Rep. Mickey Whatley's signature on it, said Campsen "got a few things accomplished" as a House member but they were in Campsen's "own self-interest." Whatley was in the House during Campsen's three terms.

A message left at Whatley's home Tuesday was not immediately returned.

The letter criticizes Campsen for the dispute with the federal government and said that while Campsen was a House member he was pushing a "narrow Christian Coalition agenda with bills such as the ban on medical cloning."

Campsen, who shared an office with Whatley at the Statehouse, said he spoke with Whatley last weekend. Whatley, Campsen said, gave approval to use his signature on an endorsement letter but didn't authorize the letter's content.

"I knew that letter didn't come from Mickey when it came out," Campsen said. "Mickey has never said anything but great things about me."

Kuhn said his campaign handled the letter and he didn't know whether Whatley had written it himself. However, he said the letter is a "red herring to try and shift focus from the real issue: My opponent had no problem using political power for personal gain at the taxpayers' expense."

Kuhn said he's simply trying to inform voters about Campsen.

"The issue of his using political power and influence for his family business is a matter of public interest," the senator said.