The emergence of Sarah Palin as a political force in the presidential race has left many top Democrats fretting that, just two weeks after their convention ended on an emotional high, Barack Obama's campaign has suddenly lost its stride.
Obama has responded aggressively this week to Palin's presence on the Republican ticket, using TV ads and campaign rallies to attack her contention that she is a political reformer who will take on the Washington establishment -- a role Obama has long claimed as his alone.
But some Democrats are now worried about the perils of Obama's strategy, saying that his campaign, instead of engaging the Alaska governor, should avoid any move that draws more attention to her and could enhance her appeal among the white, blue-collar voters who remain cool to Obama's candidacy.
A series of new polls suggests that Palin has given a major boost to John McCain's campaign, exciting the GOP base, winning over white women and all but erasing Obama's lead.
Concern among Democrats was high enough Tuesday that Sen. Richard J. Durbin (D-Ill.), one of Obama's strongest supporters, felt it necessary to cite historical polling data at a lunch of Democratic senators to convince them that post-convention "bounces," such as the one that has followed last week's GOP convention, have often faded in past elections.
To reassure nervous lawmakers, Durbin also reviewed Democratic registration gains this year in key battleground states.
Still, Democrats expressed anxiety about the new challenge suggested by recent surveys showing McCain has gained ground among independent voters and women, who could decide the race in states such as Ohio, Michigan, Pennsylvania and Virginia.
A new Wall Street Journal/NBC News poll released Tuesday, for instance, shows that McCain is now winning among white women 52% to 41% after having been statistically tied with Obama in that crucial category just a month ago.
"Whenever you see that kind of movement, you ought to be concerned; you ought to try to address it," said Rep. Elijah E. Cummings (D-Md.), a strong Obama backer.
David Bonior, the former Michigan congressman who managed Democrat John Edwards' unsuccessful presidential bid, called the new poll findings a "real concern," adding: "We can't lose white women and expect to do well in this race."
One Democratic operative familiar with the campaign's deliberations worried that the "freshness, newness and aura around Barack has been eclipsed. The campaign has been knocked off stride."
Another explained that Democrats expected Palin to "have the opposite effect" and drag McCain down, adding: "Whenever there is conventional wisdom in Washington and it's wrong, that shakes people up."
The two Democrats, like others interviewed for this story, requested anonymity in order to speak about internal campaign strategy.
Obama over the last two days has begun vigorously attacking Palin for decisions she made as governor and has tried to tarnish her image as a political maverick and reformer, highlighting, for example, her initial support for the "bridge to nowhere."
One new TV ad released this week accuses Palin of lying in claiming to have killed the $398-million link between Ketchikan and its island airport. McCain has ridiculed the project as an egregious example of the kind of pork-barrel spending he has long fought.
Palin has made her opposition to the federally funded bridge a staple of her stump speech, even though she defended it in her 2006 campaign and did not kill it until it was clear that Congress would not pay for it.
Also, Obama and his aides have started using increasingly aggressive language in recent days to denounce Palin's and McCain's attempts to cast themselves as harbingers of change.
The typically even-keeled Obama on Tuesday night invoked an old cliche and accused Republicans of trying to put "lipstick on a pig" in their adoption of the change mantra, noting that not long ago McCain had tried to present himself as the candidate of experience.
Republicans seized on the comment and tried to portray it as a sexist allusion to Palin, who in her convention speech said that the difference between a hockey mom and a pit bull was lipstick.
Obama aides waved off the attacks as a "pathetic attempt to play the gender card."
It was not clear late Tuesday whether the lipstick spat would garner much attention, but the exchange demonstrated the challenges facing Obama as the McCain camp tries to squeeze every possible advantage out of the Palin candidacy.
Some Democrats are eager for Obama to be even harder on Palin.
Rep. Chris Van Hollen (D-Md.), chairman of the Democratic Congressional Campaign Committee, said that independent voters' enthusiasm for Palin will fade when her conservative record is better known. "They need to get that information out, and they need to get it out quickly," he said.