DENVER -- The weather here was sunny this week, up to 85 degrees on the day before Mitt Romney had his first face-to-face confrontation with President Barack Obama.
But as they were debating, a cold front moved in from the mountains, plunging temperatures near the freezing mark before the night was over. By then, the atmospherics of the presidential race had been transformed as well. Mr. Romney's feisty performance gave new vitality to a campaign that had been buffeted by swing state poll numbers and the repercussions of the pirated videotape that showed the Republican seeming to dismiss 47 percent of the electorate.
As the debate headlines, with uniformly dismal reviews for the incumbent, were being published, the challenge for the Obama campaign was to see that the debate was a passing storm rather than the catalyst for a more enduring change in the political season.
In a conference call on Thursday, David Axelrod, Mr. Obama's chief strategist, was forced to offer grudging praise for the challenger's performance.
"Gov. Romney came to give a performance and he gave a good performance and we give him credit for that," he said. "The problem is, much of it wasn't rooted in fact."
Hours earlier, his GOP counterpart, Stuart Stevens, insisted that a focus on the 90 minutes at the University of Denver missed a larger point that the campaign would try to drive home in the coming weeks.
"I don't think President Obama particularly had a bad debate; he had a bad four years," he said. "He's unable to speak to it and speak to what's happening in the country and the future."
A re-energized Mr. Obama did a better, if belated, job of rebutting the Romney attacks before he left Denver, mocking his opponent before thousands of cheering and chilled supporters at an outdoor rally in a park.
"The man on stage last night, he does not want to be held accountable ... for what he's been saying of the last year," Mr. Obama said. "If you want to be president, you owe the American people the truth. Here's the truth: Gov. Romney cannot pay for his $5 trillion tax plan without blowing up the deficit or sticking it to the middle class.
"We can't afford to go down that road again," he said. "We can't afford another round of budget-busting tax cuts for the wealthy. We cannot afford to double down on the same top-down economic policies that got us into this mess."
In the conference call earlier, Mr. Axelrod signaled the new line of attack that the Democrats hope will blunt any momentum that Mr. Romney carried out of the debate. The Obama campaign's assault on Mr. Romney has always targeted his character. Now, Mr. Axelrod said they would focus on his honesty.
"We're going to hold Gov. Romney accountable for the things he said last night.
"He's completely untethered from the truth," Mr. Axelrod contended. "What we learned is that he'll say anything."
Among Mr. Romney's effective moments on the stage was his portrayal of the Massachusetts health care legislation that Mr. Obama said was a template for the federal law, Obamacare. The former Massachusetts governor rejected the comparison on substance, and also contrasted the manner in which the two laws were enacted. He noted that the Bay State plan had been passed with broad bipartisan support while Mr. Obama had to push through the administration's health legislation without any GOP backing.
The Massachusetts law had been problematic for Mr. Romney in the primaries as conservatives such as former Pennsylvania Sen. Rick Santorum contended that it would hamstring GOP efforts to criticize Mr. Obama on the controversial federal law. That didn't prove to be the case Wednesday night.
And if his self-portrait as a moderate practiced at working across party lines posed any problems for Mr. Romney's standing with the GOP's more conservative base, that wasn't apparent Thursday. The former governor started his day with a surprise appearance at a meeting of the Conservative Political Action Conference in Denver.
Afterward, he headed across country to campaign in Virginia, one of the key battlegrounds in a political map of competitive states that has remained fairly stable -- and seemingly tilted toward Mr. Obama -- for months.
While acknowledging the perception that Mr. Romney had won the debate, Mr. Axelrod consoled himself with the observation that a CBS poll suggested that although a clear majority of respondents thought that Mr. Romney had won the debate, it had not changed many voting decisions.
If he is wrong, and the strong reviews for the GOP hopeful are a prelude to a sea change in the race, one of the first places it is likely to be apparent is Pennsylvania. The Romney campaign has seemed to de-emphasize the traditional swing state this year in the face of polls showing a consistent lead for the president. If the Romney campaign senses that its opportunities are increasing, Pennsylvania could re-emerge as a tempting target.
If both campaigns suddenly begin advertising in and traveling to states beyond the nine or 10 battlegrounds they have focused on so far, that would be clear evidence that the debate had begun the process of altering a political landscape that has so far favored the president.
Politics editor James O'Toole: firstname.lastname@example.org or 412-263-1562.