In a presidential campaign freighted with war, recession and energy woes, a jibe featuring Paris Hilton, of all things, seems to have struck a nerve in Democrat Barack Obama.

For the second time in two weeks, he aired a TV ad Monday rebutting Republican John McCain's claim that Obama is little more than a celebrity, like the blonde hotel heiress.

The first time, Obama dismissed the assertion as "baloney." On Monday, Obama took a different tack with a commercial that says McCain, not he, is "Washington's biggest celebrity."

The back-and-forth may seem as frothy as a boardwalk milkshake in mid-August. But it suggests McCain is making some headway in trying to fight the campaign on his terms.

For weeks, Obama has tried to frame the election largely as a referendum on President Bush, using every chance to tie McCain to the unpopular incumbent. McCain has tried to make it about Obama by arousing concerns about the first-term senator's experience and depth.

McCain has aired a series of TV ads that showed far more images of Obama than himself, a somewhat risky approach. All of them tried to turn Obama's crowd-pleasing talents against him.

A July commercial blaming Obama for high gasoline prices — which the watchdog group FactCheck.org called "a tank full of nonsense" — portrayed crowds chanting Obama's name. A subsequent ad mixed images of Obama on his recent European trip with video clips of pop figures Hilton and Britney Spears.

Obama is "the biggest celebrity in the world," the announcer said. "But is he ready to lead?"

Even some Republican strategists questioned whether the strategy was smart or dignified. And Hilton herself produced a video poking fun at McCain that drew large Internet viewership. But Obama's latest ad suggests the "celebrity" taunt has some sting, and efforts to dismiss it as silly have not been effective.

"They woke up this weekend and figured out that that ad resonated and they needed to do something about it," said Terry Holt, a Republican strategist.

Although the McCain campaign was lampooned for its Hilton ad on late night television and blogs, it kept hammering at the celebrity theme. A McCain TV ad introduced last week showed Obama waving to cheering crowds, along with his picture on the covers of the magazines GQ, US Weekly and Vanity Fair.

In his new ad, Obama tries to turn the celebrity theme to his advantage, grafting it to his claim that a McCain presidency would amount to a third term for Bush. That claim has generated a defensive response from McCain.

McCain daily tries to beat back the idea that he'd represent a continuation of Bush, as he did Monday while campaigning in Erie and Harrisburg, Pa. Nearly 85 percent of Americans think the country is on the wrong track, McCain told workers at an Erie manufacturing facility, and "we've got to reform and reform and reform."

The new Obama ad shows McCain hugging Bush while the voiceover says, "as Washington embraced him, John McCain hugged right back."

Obama spokesman Bill Burton said the ad is designed to say voters have a choice between Obama, who stands for change, and McCain, "who overwhelmingly favors the status quo."