And a series of quick polls taken after the Republican convention have suggested that Mr. Obama has lost support among white women and independent voters. Polls taken so close to major political events are notoriously unreliable, but Democrats remember what happened in 2004, when Republicans used the period right after Senator John Kerry’s nomination to undercut him with a series of attacks.

By every indication, Mr. Obama’s aides underestimated the impact that Mr. McCain’s choice of Ms. Palin would have on the race. Mr. Obama and his campaign have seemed flummoxed in trying to figure out how to deal with her. His aides said they were looking to the news media to debunk the image of her as a blue-collar reformer, even as they argued that her power to help Mr. McCain was overstated.

“Everyone was astonished that she drew 9,000 people to Lancaster the other night,” said Mr. Obama’s senior strategist, David Axelrod. “But we drew 10,000 people there last week.”

“They got a transient boost from the sort of imagery surrounding her selection,” Mr. Axelrod said. “But I think things will settle in. She will be a candidate and not just a symbol.”

Beyond that, Mr. Obama’s aides said they had been taken aback by the newfound aggressiveness of the McCain campaign under Steve Schmidt, who has played an increasingly powerful role since last summer. Even as the aides have denounced the tactics as unsavory, they acknowledge that Mr. McCain is running a more effective campaign than he was a month ago.

“They had big problems in their campaign, and they made adjustments,” Mr. Axelrod said.

To a large extent, the perception that Mr. Obama is struggling is based on national polls taken in the days after the convention. But Mr. Obama’s campaign views such measures as irrelevant and focuses on what is going on in the 18 or so swing states.

Mr. Plouffe argued that the attention being paid by national news media outlets to events like Mr. Obama’s lipstick comment was not mirrored in local news coverage. What is more, the Obama campaign has filled the airwaves in some states with advertisements that link Mr. McCain and Mr. Bush.