"I do," Sanford said, taking his oath.
"Congratulations, you are now a member of the 113th Congress," House Speaker John Boehner said.
With that, the saga of the gifted politician, husband and father who served three terms in the House beginning in 1995, went on to become governor and threw it all away for his now-fiancee Maria Belen Chapur, came full-circle. A week earlier, he had defeated Democrat Elizabeth Colbert Busch, the sister of political satirist Stephen Colbert, in a special election.
"I'm simply humbled to be here," Sanford told the House, noting two sons watching from the gallery along with Chapur. "I stand before you, I guess, with a whole new appreciation for a god of second chances."
The story of Sanford's rise, fall and return to Washington is freighted with melodrama.
He was thrust into the national spotlight when, as governor, he disappeared for five days in 2009, telling his staff he was hiking the Appalachian Trail. The father of four later admitted in a tearful news conference he'd been in Argentina with Chapur. He called her his "soul mate" and became the butt of jokes by late-night TV comics.
His wife and political ally, Jenny, divorced him and later wrote a tell-all book about their relationship.
Sanford, for a while, disappeared from political life.
But then Rep. Tim Scott, R-S.C., was appointed to replace retiring Sen. Jim DeMint, sparking a special election. Sanford jumped in the race, supported by the National Republican Campaign Committee.
Three weeks before the election, the NRCC pulled its support after his ex-wife filed a court complaint alleging he was in her house in violation of their divorce decree. Even some of Sanford's allies held him at arm's length. Sanford defeated Colbert Busch anyway, with 54 percent of the vote.
Sanford's return sets up an awkward dance with congressional Republicans, but on Wednesday, everyone was pledging to work together.
"If there's anybody who believes in putting the past behind them, it's me," Sanford said. "I don't begrudge anybody for doing what they felt they needed to do at a given moment in time. I look forward to working with each of them."
House Republicans, too, seemed eager to leave the unpleasantness behind.
"The voters of South Carolina made their decision, and we're going to welcome him to our conference," said Rep. Cathy McMorris Rodgers of Washington, vice chair of the House Republican Conference.
"House Republicans' outreach to women voters now has Mark Sanford as the face," said Rep. Steve Israel, the chairman of the Democratic Congressional Campaign Committee, said after Sanford's victory. "Republicans now have to defend him and stand with him until Election Day."
For now, the back-again congressman and his fiancee savored the day.
Sanford has a lighter side, too. Known for his frugality and fiscally conservative views, Sanford slept on a futon in his House office to save money during his earlier terms in Congress. As governor, he brought two pigs named Pork and Barrel to the Statehouse to protest legislative spending.
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