Gov. Sarah Palin did what she had to do in Thursday's vice presidential debate. She didn't stumble or make any major gaffes. She was folksy and friendly, deflecting questions for which she was unprepared. In short, she restored her political credibility, which had been seriously compromised in the past few weeks. What she did not do, in my view, was win the debate.

Sen. Joe Biden gave one of the best political performances of his life and, on both substance and style, was the clear winner. Whether the debate was a game-changer is another matter. I tend to think not. The game has already changed, with the major battleground states swinging toward Sen. Barack Obama.

The debate was all about Palin, not about Biden. As many observers noted, Biden's main objective was to do no harm. In fact, the main objective of any vice presidential candidate is to do no harm. After more than 30 years in the Senate, there are no questions about Biden's qualifications for the vice presidency. All he had to do was to avoid any of his famous gaffes (which for some people are an asset). Nor could he appear to be too hard or too soft on Palin. He, too, exceeded expectations.

Palin was in an entirely different position. After a spectacular debut at the Republican convention, her recent on-the-record interviews have been less than successful. Many observers, including some conservatives, think they were disastrous, raising fundamental questions about her readiness to be the vice president. For some, she was becoming a national embarrassment. Perhaps more telling, Palin appeared to have lost her trademark self-confidence.

Thus, she faced a much more daunting task than did Biden. She had to show that she was competent, aware of the issues and ready to serve. Her performance, one way or another, inevitably would reflect on the judgment of Sen. John McCain. As she initially rallied the base of the party at the convention, his judgment was seen to be excellent. But as she sank in the polls, his judgment was called into question. Coming after a bad two weeks of financial crisis, in which McCain seemed confused and indecisive, a Palin failure in the debate would be serious.

Clearly, she didn't fail, though she is not yet in Biden's league. More important, Palin seemed to have regained her self-confidence. She did herself a lot of good as a result of the debate. Whether she did McCain's candidacy any good is another matter. By way of contrast, a failure for Biden would have been relatively inconsequential. As it turned out, Biden did exceptionally well.

One remarkable contrast between the presidential and vice presidential debates was the warmth and passion displayed by both Palin and Biden. The two actually looked at each other. As a result, the debate atmosphere was much warmer and friendlier than it was between Obama and McCain, when McCain steadfastly refused to look at Obama.

Palin connects on a personal level. It is probably her greatest political strength. It is one of Biden's strengths as well. He teared up when talking about the challenge of being a single father following the tragic deaths of his first wife and his daughter, not knowing whether his badly injured sons would make it or not. Talking about it with restraint and sincerity makes good political theater, just as it does when McCain talks about his years as a prisoner of war. These two men have suffered, and Americans admire them for it. It lends them personal gravitas.

Though it is still too early to say if the move is permanent, the financial crisis seems to have shifted the political momentum in favor of Obama. The McCain campaign has already abandoned the state of Michigan.

Moreover, the voter-registration rolls in several competitive states show more new Democrats than Republicans. Iowa and Nevada, two states that went for George Bush in 2004, have reversed a long-standing trend and now show more registered Democrats than Republicans.

Much can change in a month, of course, and at this point the election is still close. But the current trends do not favor McCain or the Republicans. That has been true for some time. The question has been, in view of these trends, why hasn't Obama shown greater strength?

In early October, with the election only a month away, Obama at last seems to be pulling ahead.

William M. Stewart, a former U.S. Foreign Service officer and Time magazine correspondent, lives in Santa Fe. He writes weekly on foreign affairs and politics.