All the leading candidates for president who have contested primaries eventually find themselves where Mitt Romney finds himself today: facing a crisis of political credibility. Romney’s inevitability was punctured by his poor performance in the waning days of the South Carolina primary.

There are circumstances unique to South Carolina — its extraordinarily high evangelical and conservative vote — to explain away the loss. Romney, in theory, is headed to happier hunting grounds in Florida and beyond in Michigan and Nevada. There is also comfort for Romney supporters in his superior campaign cash position and superior organization. If, to Democrats’ delight, we are headed for a long war of attrition for Republican delegates, then Romney would still seem the best positioned to win.

But none of this analysis gets to the heart of this possible turning point in the Republican race. This moment is all about Romney. Does he have the strength and smarts to adapt and take back the race? Can he regroup and restore confidence in his candidacy?

It isn’t accurate to draw many answers to these questions based on the past 36 hours. It usually takes a few days for candidates who have been rocked to regain their balance. But I must add that in his few public appearances since his South Carolina drubbing, Romney has not inspired. He suddenly seems weak and more beatable, but, of course, defeat will do that to you.