From the “Department of What Was He Thinking?!” here comes South Carolina’s Republican governor and a GOP hopeful for president, admitting that his five-day off-the-radar escapade was to visit his Argentine lover–not to hike the Appalachian Trail, as aides said. Unbelievable. Or, well, all-too-believable in the world of right-wing, Bible-thumping, family values Republican politics these days. (viz. Sen. John Ensign, e.g.)

From the NYT:

COLUMBIA, S.C. — Mark Sanford, the governor of South Carolina, said he had conducted an extra-marital affair with a woman in Argentina, ending a mystery over his week-long disappearance that had infuriated lawmakers and seemed to put his rising political career in jeopardy. He apologized for the affair and the deception surrounding his trip in a rambling, nationally televised news conference Wednesday afternoon.

Governor Sanford, 49, admitted that he had been in Buenos Aires since Thursday, not hiking on the Appalachian Trail as his staff had told reporters.

In revealing an affair that had gone on for about a year — and which he said he had disclosed to his wife, Jenny, five months ago — he said: “This was selfishness on my part.”

Mr. Sanford announced on Wednesday that as a result, he was resigning his position as chairman of the Republican Governors Association. His second — and final — term leading the state of South Carolina ends in 2011.

It took him more than a few stumbling minutes to get to the crux of the matter.

“The bottom line is this,” he said. “I have been unfaithful to my wife.

“I developed a relationship with what started as a dear dear friend from Argentina,” Gov. Sanford said. “It began very innocently, as I suspect these things do, in just a casual e-mail back and forth. But here, recently, over this last year, developed into something much more than that. And as a consequence, I hurt her. I hurt you all, I hurt my wife. I hurt my boys. I hurt friends like Tom Davis. I hurt a lot of different folks.”

Surrounded by more than 50 reporters, photographers, aides and spectators in the rotunda of the South Carolina statehouse, the governor spoke with a quiver in his voice and was visibly shaken, tearing up at times and rocking on his feet at the podium. He pleaded with reporters not to pester his family: “I would ask for y’all’s indulgence, not for me, but for Jenny and the boys.”

Jenny and the boys were not there. Three of his sons are teenagers, and his youngest is 10 years old. And he was out of touch over Father’s Day. Sounds awful. At least Wilbur Mills didn’t travel so far to embarass himself with an “Argentine Firecracker.”

Chris Cillizza at the WaPo analyzes the fallout in The Fix:

• Sanford was clearly unprepared for the media swarm he faced. He began shakily with a riff about his time spent hiking the Appalachian Trail before rolling off a long litany of people to whom he needed to apologize. Sanford, usually an extremely confident public orator, stumbled over his words time and time again and continued to take questions well after he had promised a “last question.” (In Sanford’s defense, it’s hard to imagine anyone would be prepared to make such an announcement.)

• This is not the end of the story. The problem for Sanford is that he appears to have willfully misled his staff, the lieutenant governor and the people of the state about his whereabouts — signaling that he was likely headed to the Appalachian Trail before hopping on a flight to Argentina. There will almost certainly be some sort of investigation into whether Sanford misused state funds on this trip — remember that he took a state-owned vehicle and parked it at the Columbia airport — that will keep this wound raw for the foreseeable future.

• Sanford’s 2012 candidacy is almost certainly over. Having an extramarital affair is bad, but not being truthful to the people of the state and disappearing for five days is unforgivable on the national stage — or any stage for that matter. Let the search for a new champion for fiscal conservatives begin!

• Coming nearly one week to the day after Sen. John Ensign (R-Nev.) admitted his own affair, this is yet another gut punch for the Republican Party, which can’t seem to get off the mat. Republican strategists have to be wondering when enough is enough; the spate of bad press for the party for the past few weeks has been unrelenting.

Okay, so who’s next?