WASHINGTON (CNN) -- Sen. John McCain's recent campaign commercial linking Sen. Barack Obama to vapid celebrities was unanimously criticized in Democratic quarters, but one of the party's leading strategists said it did the job.
While acknowledging her supporters' anger, Hillary Clinton says she wants unity behind Barack Obama.
In an op-ed in Politico on Tuesday, Mark Penn, former top strategist to Sen. Hillary Clinton, said negative ads are often effective in forming public opinion of a candidate. He pointed to the McCain campaign's recent ad featuring Paris Hilton and Britney Spears as an example of an effective television spot.
"Fair or not, as advertising it did its job: It used humor, stuck viewers with memorable images and created a debate, just as Lyndon Johnson's 1964 'Daisy' ad, Walter Mondale's 'Red Phone' spot 20 years later and Hillary Rodham Clinton's '3 a.m.' commercial in 2008 did," Penn wrote.
Penn, who was behind Clinton's headline-grabbing "3 a.m." ad that questioned Obama's readiness to lead during a national security crisis, also said the Illinois senator should have responded more effectively to the Hilton/Spears ad.
"The Paris Hilton ad also bore a Republican political trademark -- attacking a candidate's strengths rather than the candidate's weaknesses," Penn wrote. The spot attempted to portray Obama's leadership for change as something fluffy and useless. Obama did not immediately hit back on the air." Watch Obama's response to reporters »
Penn, who was ousted from his formal role with the Clinton campaign last spring, faced fresh criticism earlier this week after newly released campaign memos revealed that he advocated painting Obama as foreign.
"His roots to basic American values and culture are at best limited. I cannot imagine America electing a president during a time of war who is not at his center fundamentally American in his thinking and in his values," Penn wrote in a March 2007 memo to campaign colleagues. Watch more on the leaked e-mails »
"All of these articles about his boyhood in Indonesia and his life in Hawaii are geared toward showing his background is diverse, multicultural and putting that in a new light. Save it for 2050," the memo added.
The e-mails shed light on a bigger problem plaguing Democratic Party stalwarts: how best to bring Clinton supporters into the Obama column. Watch more on the unity problems that Democrats face »
Obama has said, however, that he doesn't anticipate "any problems."
But Obama's assessment runs counter to grumbling from some of Clinton's supporters, some peculiar praise from the former president and Sen. Clinton's seeming embrace of a plan to put her name into nomination.
In the modern era of presidential primaries, no losing candidate has so visibly endorsed an opponent so many months before the convention and still put his or her name up for nomination.
"I happen to believe that we will come out stronger if people feel that their voices were heard and their views were respected," the senator from New York has said of some of her supporters, who are demanding a role in the party's convention.
A video posted on YouTube showed Clinton talking to supporters who wanted to have her name put to a vote at the convention.
"I know from just what I'm hearing, there's incredible pent-up desire, and I think that people want to feel like, 'OK, it's a catharsis, we're here, we did it, and then everybody get behind Sen. Obama,' " she told the crowd.
Obama said last week that the brouhaha over whether Clinton's delegates would be able to vote for her at the Democratic convention was a media creation. "There hasn't been controversy other than what you guys are projecting right now," he told reporters Thursday.
Obama described conversations between the two campaigns over convention planning as "seamless."
"It has not been a problem," he added.
On Friday, Clinton seemed to agree. At an Obama rally in Las Vegas, Nevada, she said, "We had a hard-fought campaign, and it was exciting. It was a bit like the proverbial roller coaster, but we are now unified and ready to go forward together.
"And it is imperative that each and every one of us think about how we're going to help in this election," she said. Watch more of Clinton's speech »
"We are one party, we share one vision, and we believe as Democrats, as independents and repentant Republicans, in the progress we can make together!"
CNN's Ed Hornick and Alexander Mooney contributed to this report.