WASHINGTON — Photos flash of Paris Hilton and Britney Spears. Crowds roar and lights pop. "He's the biggest celebrity in the world," says a woman's voice.
Then it becomes clear: The TV ad is not about a tabloid personality -- it's about Barack Obama.
In launching a negative ad Wednesday that it says will run in 11 states, John McCain's campaign gave its clearest signal yet that its main focus right now isn't talking about the presumed Republican nominee. Instead, it is trying to shape the public image of Obama -- in this case, by comparing him to two celebrities who are widely mocked as lacking substance.
The Obama camp also has worked hard in recent days to mold his public persona, showcasing him overseas with a succession of world leaders, then back home with former Treasury secretaries and a former Federal Reserve chairman.
With fewer than 100 days until ballots are cast, the presidential race chiefly appears to be a fierce battle to define the presumptive Democratic nominee for voters unsure about his abilities and values.
"Right now, both campaigns have to do the same thing, which is establish who Barack Obama is," said Neil Newhouse, a Republican pollster based in Virginia. "That's the real battle going on."
In trying to paint its image of Obama, the McCain camp has turned increasingly negative, even derisive. Obama, meanwhile, is still working to persuade voters to trust him enough to see him as a president, even after 18 months of largely positive publicity.
Each candidate's tactics pose clear dangers, party insiders and analysts say.
For Obama, the efforts to portray himself as presidential -- holding news conferences overseas, for example, or briefly using a campaign emblem similar to the White House seal -- run the risk of appearing arrogant or presumptuous.
"It's a fine line he's walking, which is to display confidence and self-assurance without appearing cocky and overconfident," said Ross K. Baker, a political science professor at Rutgers University in New Jersey. "Some people inevitably will judge him to be on the wrong side of the line."
For McCain, the new and sharply negative tone toward Obama could damage the Republican's image as a maverick who rejects the attack-dog politics of traditional Washington.
The Arizona senator's new TV ad shows pictures of Obama's speech last week to an estimated 200,000 people at an outdoor event in Berlin, comparing his celebrity to that of pop culture figures Hilton and Spears. "But is he ready to lead?" it asks.
In addition to launching the ad, McCain recently has accused Obama of being willing to lose the war in Iraq in order to win the November election. Over the course of several days, he also has attacked Obama for canceling a visit to wounded U.S. soldiers at a military hospital because he couldn't bring reporters along. Obama's campaign has angrily disputed the charge as false and misleading.
David Winston, a GOP operative in Washington, argues that McCain has erred by issuing negative personal attacks. McCain should put Obama on the defensive by highlighting their policy differences on taxes, energy and national security, he said.
"He's not emphasizing the contrasts that can actually help him win," Winston said.
Turning an opponent's strength into a weakness is basic political strategy. McCain rarely draws large or boisterous crowds, as Obama did in Berlin. Even close aides acknowledge that McCain's public speaking skills pale beside Obama's soaring rhetoric. McCain drew far less attention during his own foreign travels, to Canada, Mexico and Colombia in June and July.
Public opinion surveys cannot determine whether McCain's increasingly pointed criticism of Obama is having an effect. But polling does suggest that voters are spending time trying to form an opinion of Obama. In a Wall Street Journal/NBC News poll released last week, 51% of people said they were focusing more on what kind of president Obama would be than McCain; 27% said they were focusing more on McCain.
That finding is to be expected, as Obama is a first-term Illinois senator and a fresh face, whereas McCain has spent decades in the national spotlight. But it also helps explain why Obama's image is now the focus of both campaigns.
GOP strategists say Obama's failure to gain significant ground in opinion polls since his trip to Europe, Afghanistan and the Middle East suggests the steady hammering has paid off.
"I'm one of those who thinks McCain needs to be very aggressive at this point," said Ken Khachigian, a veteran GOP strategist based in Orange County. Despite the risk of appearing too negative, he said, McCain needs to convince voters that Obama "is not one of us. He's got to portray Obama as out of touch."
McCain continued his attacks Wednesday while speaking to workers at a machine maintenance company in suburban Denver. He called Obama a politician who "puts self-interest and political expedience ahead of problem-solving."