In April, Jenny Sanford accused him in a court complaint of repeatedly trespassing in her home. The revelation prompted the National Republican Congressional Committee to pull its support from Sanford's campaign. Sanford has said he went there because he didn't want his 14-year-old son to have to watch the Super Bowl alone.
Even with the attacks heating up, Sanford has some advantages going into the campaign's final week. He held the same congressional seat in coastal South Carolina for three terms in the 1990s before serving two terms as governor. On the campaign trail, he has touted his conservative credentials as a budget-cutter.
"Unless we get our fiscal house in order in Washington," he told a chamber of commerce group Tuesday, "there will be profound consequences for the American way of life."
Paul, a Kentucky Republican, praised those credentials Tuesday in issuing his endorsement, saying Sanford is an advocate for limited government and cutting spending.
"Mark has proven during his time in office that watching out for the taxpayers and holding the line on spending are his top priorities," Paul said.
"I think in looking at my own record there's been a consistent theme of looking out for the taxpayers and the bottom line," Sanford said in thanking Paul for the endorsement. "Unfortunately, with respect to my opponent, it simply isn't believable she would be an independent voice given who has been funding her campaign."
Sanford has tried to put the focus on Colbert Busch, asserting that political out-of-state interests are funding her campaign. She has said she would be an independent voice answerable only to the people of the district.
On Wednesday, Sanford gets a boost from his successor, Republican Gov. Nikki Haley. She will make her first campaign appearance on behalf of her former mentor at a Sanford fundraiser at a home on the city's famous Battery.
"Nikki believes it is critical that South Carolina speak with as much unity as possible on key federal issues facing our state, such as labor union powers, Obamacare, and deficit spending," said spokesman Tim Pearson. "Mark Sanford is clearly the candidate who will stand with our Congressional delegation in fighting Washington's overreach."
Colbert Busch, Sanford and Green Party candidate Eugene Platt are on the ballot in the May 7 special election. The vacancy was created by the appointment of Republican Tim Scott to the U.S. Senate.