“We reached a point where I felt it was important to look my sons in the eyes and maintain my dignity, self-respect, and my basic sense of right and wrong,” she said. Because of the separation, she said, she did not know where he was in the last week.  The governor, who raised his national profile by opposing the Obama administration’s economic stimulus plan, said he would resign from his position as chairman of the Republican Governors Association. He will be succeeded by Gov. Haley Barbour of Mississippi. A reporter tried to ask Mr. Sanford if he would resign from the governor’s office, but he did not answer.  Coming a week after the admission of an extramarital affair by Senator John Ensign, a Nevada Republican who had also begun exploring a presidential run in 2012, the governor’s acknowledgment was yet another blow to Republican hopes for a strong field of challengers to President Obama.  “Personal circumstances over the course of the last week have managed to shrink the front line of the 2012 possible contender list by 30 percent,” said Phil Musser, a former executive director of the Republican Governors Association.  Mr. Sanford is regarded as a political lone wolf and has made numerous enemies even within his own party, which controls both houses of the state legislature. Scott H. Huffmon, a political science professor at Winthrop University in Rock Hill, S.C., said it was unclear whether there would be pressure on the governor to resign. “His opponents,” Dr. Huffmon said, “are sitting back trying to figure out if they’d be better off with a completely emasculated governor to deal with or if they’d be better off with André Bauer,” the lieutenant governor, who would take office if Mr. Sanford resigned.  Mr. Sanford made at least one state-sponsored trip to Argentina during the period of his relationship. In an interview late Wednesday, Daniel Scioli, the governor of Buenos Aires Province, said he met with Mr. Sanford on June 26, 2008, in La Plata, a town outside Buenos Aires. Mr. Scioli said the request for the meeting had come from Mr. Sanford’s office via the United States Embassy.  The governor was not known as a moralist but has frowned on infidelity and as a congressman voted to impeach President Bill Clinton after the Monica Lewinsky affair. “He lied under a different oath, and that’s the oath to his wife,” Mr. Sanford said at the time on CNN. “So it’s got to be taken very, very seriously.”  Mr. Sanford and his wife had joined an intensive Bible study group for couples in the last few months, according to William H. Jones, president of Columbia International University, a conservative evangelical college. Dr. Jones said the governor and his wife had been encouraged to join the Bible study by a longtime friend, Cubby Culbertson, a businessman in Columbia who teaches the Bible and who was thanked by the governor in his news conference.  At the news conference, Mr. Sanford said his friendship with the unnamed woman began eight years ago and became a romance about a year ago. He said he had seen her three times since then. The relationship was “discovered” five months ago, he said, and he had been trying to reconcile with his wife.  Mr. Sanford strongly implied that he had ended the affair. “The one thing that you really find is that you absolutely want resolution,” he said. “And so oddly enough, I spent the last five days of my life crying in Argentina.”  On Wednesday afternoon, The State, the leading newspaper in Columbia, published on its Web site several e-mail messages it said it obtained in December between Mr. Sanford and a Buenos Aires woman the newspaper identified only as Maria.  In one of the messages, the governor describes himself as being in a “hopelessly impossible situation of love” and stops just short of going into what he describes as sexual details of their encounters.  After a barrage of news media requests about the missing governor began Monday, the governor’s spokesman, Joel Sawyer, released a statement on Monday afternoon saying that the governor was taking some time to recharge after the stimulus battle and to work on “a couple of projects that have fallen by the wayside.” Ms. Sanford told The Associated Press that her husband had gone somewhere over the Father’s Day weekend to write, but that she did not know where.  Mr. Sawyer played down the controversy as a creation of Mr. Sanford’s political enemies.  Then, around 10 p.m. Monday, Mr. Sawyer sent a “high priority” e-mail alert to reporters that Mr. Sanford was hiking on the 2,100-mile Appalachian Trail. Mr. Sawyer flatly denied a television news report that the governor had been seen boarding a plane at the airport in Atlanta.  At the news conference, the governor said his staff members had based their statements on tentative scheduling information he had given before he left.  Mr. Sanford’s rivals immediately pounced on the apparent confusion in the governor’s office.  “The people of this state deserve complete honesty from Governor Sanford,” said State Senator John C. Land III, the Senate Democratic leader, in a statement issued Wednesday morning before the news conference. “Never in my 32 years as a state senator have I witnessed a governor and his staff act in a more dishonest, secretive and bizarre manner.”  But Mr. Land said that he doubted there would be pressure for Mr. Sanford to go because a resignation would mean that State Senator Glenn McConnell, the powerful president pro tem, would have to become the lieutenant governor, a relatively powerless position.  Mr. Sanford recently lost a high-profile battle to divert $700 million in federal stimulus money toward reducing the state deficit, challenging the Obama administration on the issue.  Critics said he was simply seeking to raise his national profile, but the governor maintained that his primary goal was to strengthen the executive office in South Carolina, where the governor has few powers.  Mr. Sanford has long been known as an iconoclast. As a congressman, he slept on a futon in his office. To showcase his opposition to pork-barrel spending, he once brought two live piglets onto the floor of the legislature.  Still, many were shocked by his announcement. “I never figured Sanford for anything like this, said Neal D. Thigpen, a political science professor at Francis Marion University in Florence, S.C.  Reporting was contributed by Alexei Barrionuevo in Buenos Aires; Laurie Goodstein and Liz Robbins in New York; and Jim Rutenberg in Washington.  A version of this article appears in print on , on Page A1 of the New York edition with the headline: ENDING MYSTERY, A GOVERNOR SAYS HE HAD AN AFFAIR. Order Reprints| Today's Paper|Subscribe
In a rambling news conference, Mark Sanford apologized for having an affair, dampening his prospects for a national political career.