Fellow Republicans issued sharp calls for the disgraced Sanford to step down - a move he indicated he was not considering. And at least one campaign donor was drafting a letter asking for his money back.
One county GOP leader said the governor "talked about how our leaders have stepped away from our core values, and said one thing on the campaign trail or out in the public and did something different in the background."
Glenn McCall, a local representative to the Republican National Committee, said the GOP "can recover from this if we hold him accountable and the governor does the right thing and resigns for the sake of the party."
Sanford emerged briefly Thursday from his family's home on Sullivans Island, off the coast from Charleston, and rolled down the window of his car to talk. Asked if he planned to resign, he shook his head no.
Sanford also issued a statement promising to reimburse the state for an economic-development trip he took to Argentina last year that included time spent with his mistress. State Commerce Department records indicate more than $8,000 was spent on airfare, lodging and meals, though Sanford did not say how much he will pay back.
After disappearing to Buenos Aires for almost a week, Sanford returned Wednesday to reveal the affair and publicly apologize to his wife and four sons, his supporters and constituents. He also resigned as chairman of the Republican Governors Association.
His emotional news conference had even harsh critics holding their fire, saying they were praying for the family to reconcile.
But the gloves started coming off Thursday as it became clear that Sanford had used state resources on at least one trade trip that included a tryst with his lover.
Sanford donor Al Hill of Dallas-based AG Hill Partners, an investment firm, was having a letter drafted Thursday requesting that money given to the governor's campaign be immediately returned. The company gave $3,500 for Sanford's 2006 race.
"And now we are asking that it be sent back," said Joy Waller, an assistant to Hill. "Do you even have to ask why?"
Former Sen. Fred Thompson, who waged a failed GOP presidential bid last year, took Sanford to task on his Web site.
"I don't have any sympathy in a situation where you've got a wife and four fairly young kids ... don't play it out in public," Thompson said of Sanford, who had been seen as a potential candidate for the 2012 GOP presidential ticket.
Even the first lady, Jenny Sanford, seemed inclined to let her husband fend for himself, a departure for a woman who has served as his closest political adviser for years.
"His career is not a concern of mine. He'll have to worry about that," she told reporters as she drove away from the family's beach house Thursday afternoon with children in the car. "I'm going to worry about my family and the character of my children. I'm going to take it a day at a time, and right now I am going out on the boat."
The state's top senator questioned whether Sanford broke the law when he disappeared without transferring power to the lieutenant governor.
Sanford said he left his staff with the impression he was heading off for some solo hiking on the Appalachian Trail, a bogus story that they relayed to reporters who began asking where the governor had gone.
"I would think that if the evidence indicates that there is a willful effort to circumvent the constitution, I think there would be a chorus of calls for him to resign," said state Sen. Glenn McConnell, a fellow Republican.
"It's over. He ought to resign," said Furman University political scientist Donald P. Aiesi. "First, he was derelict in his duty, obviously. And secondly, if he's going to make this marriage work, that needs to be his full-time job. He doesn't need to be serving the people of South Carolina. He needs to serve his family."
State Republican Party Chairwoman Karen Floyd had an online meeting with the party's top leaders Thursday night to listen to their concerns and brief them on developments, but closed it to reporters. She said it was too early to call for a resignation, but the party could take that action when it meets in a July 6 conference call.
Sanford, barred by state law from running again, leaves office in 2010. If he were to resign, Lt. Gov. Andre Bauer - expected to run for the top spot - steps into the office.
The two men are not allies - candidates for governor and lieutenant governor run separately in the state - and others are also jockeying for the job.
There are deep misgivings about Bauer, who spent much of the 2006 campaign recovering from injuries suffered when a plane he was flying crashed. He was also injured politically by news that he had been let off for speeding after troopers stopped him. He was elected the nation's youngest lieutenant governor in 2002 at age 33.