There is a price to pay when a president appears disengaged, and President Obama obviously learned how much his diffidence cost him in the first debate this month. On Tuesday night, in the second debate, he regained full command of his vision and his legacy, leaving Mitt Romney sputtering with half-answers, deceptions and one memorable error.

Instead of windy and lethargic answers, the president was crisp in reciting his accomplishments and persuasive in explaining how he has restarted economic growth. Instead of letting Mr. Romney get away with a parade of falsehoods and unworkable promises, he regularly and forcefully called his opponent wrong. Having left many supporters wondering after the first debate whether he really wanted another four years, he finally seemed like a man who was ready to fight for another term.

What he did not do was describe how a second term would be more successful than his first has been, and, in particular, show how he would cut through the thicket of Republican opposition if re-elected. He missed opportunities to call for a more forceful opposition to assault weapons in another term, and to put forward a clear immigration policy.

But the contrast with the weak and failed ideas that Mr. Romney proposed could not have been clearer. The president noted that he had signed legislation that increased pay equity for women; Mr. Romney not only refused to say whether he would have done so, but condescendingly said he had hired many women when he was the governor of Massachusetts and had given them flexible schedules.