Washington (CNN) -- President Barack Obama's re-election campaign spent millions of dollars over the past few weeks in an advertising blitz aimed at negatively defining GOP challenger Mitt Romney -- an effort that, according to several national polls and political experts, has met with tepid results.
Those ads include a spot in heavy rotation with Romney singing "America the Beautiful" at a campaign event as out-of-context phrases from news reports such as "outsourced jobs to India" and "had millions in a Swiss bank account" appear on the screen. According to Vanderbilt University's Ad Rating Project, which polled 600 Democrats, Republicans and independents, 73% said the ad was "negative."
More than half of independents polled said they disliked the ad.
The Obama campaign is "trying to build a personality frame around Romney. 'Here's Richie Rich. He's out of touch with the public ...," said Paul Brewer, a professor and assistant director for research at the University of Delaware's Center for Political Communication.
The blitz is all about the Obama campaign's attempt to introduce Romney to the American people before the GOP candidate has a chance to introduce himself, said Kenneth Goldstein, president of Kantar Media/Campaign Media Analysis Group, a Washington-based firm that analyzes advertising spending on political and policy issues.
"There's lots of people saying it didn't move the needle at all, and there's lots of people who say the (negative campaign ads) in June had a big influence in battleground states ...," Goldstein said. "What we do know is that there was not this huge shift."
According to CNN's most recent Poll of Polls, an average of three national polls of registered voters, Obama holds a slight lead over Romney at 47% to 43%, but those numbers have stayed pretty stable during the ad blitz.
"What's interesting is that so far it hasn't seemed to move the numbers," CNN chief political analyst Gloria Borger said recently of the negative stream of campaign ads.
And that leaves a narrow sliver of undecided voters up for grabs.
"Ads matter at the margin," Goldstein said. "And this is looking like an election that is going to be deciding at the margin."
And in that, the Obama campaign might be getting more than it bargained for when it comes to attack ads, according to political experts and polling.
According to NBC News/Wall Street Journal poll released Tuesday, 32% of respondents said their view of Obama was "very negative," a number that is up six percentage points since the same question was asked in April.
Romney suffered an equally large hit, with 24% of respondents indicating they had a "very negative" view of the former Massachusetts governor. Eighteen percent had the same response in April.
The president's re-election team will spend more than $32 million in July and the Romney campaign $14 million on ads aimed largely at wooing voters at the margins, according to a Republican ad buying source. The Obama campaign was expected to spend $25 million on advertising in nine battleground states this month, including a 30-second ad that accuses Romney of outsourcing while he was head of Bain Capital.
In contrast, the Romney campaign was expected to spend $6.3 million for ad time, according to a Democratic source tracking ad buys. GOP super PAC American Crossroads spent $9.3 million this month on a new ad called "Smoke" defending Romney's record against the Obama re-election team's Bain attacks.
"What happened to Barack Obama? The press and even Democrats say his attacks on Mitt Romney's are misleading, unfair and untrue, blowing smoke, too far, no evidence," the spot says.
People are no more likely to trust or distrust "the messages of innocuously named, unknown independent groups (such as super PACs) than they are the messages of candidates," said Deborah Jordan Brooks, associate professor of government at Dartmouth College who authored a recent study on the effectiveness of super PACs. "But they are likely to punish candidates for running negative messages themselves."
And voters are none too pleased when they feel the tone of campaign ads have become too negative.
About three-quarters of Americans believe this election year is more intense in its negative campaigning than previous years, with 74% saying the problem is getting worse, according to a Knights of Columbus-Marist survey released Tuesday.
Plus, most voters already feel that there's little left to learn about the presidential candidates. In Obama's case, 90% say they already pretty much know what they need to know about him; just 8% say they need to learn more. Sixty-nine percent also say they already mostly know what they need to know about Romney, with 28% saying they need to learn more about him, according to a Pew Research Center poll.
Still, the Obama campaign began airing a much gentler ad last weekend in battleground states. In it, the president tells voters, "Over the next four months, you have a choice to make."
A senior Obama campaign official says "The Choice" ad is not a shift in tone but echoes a theme the president laid out during a speech in Ohio when he said the November election "is not simply a choice between two candidates or two political parties, but between two paths for our country."
However, the campaign official added, voters can also expect that Romney's economic record and related ads "will remain central to the discussion."
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CNN's Kevin Bohn, Ashley Killough, Adam Levy and Kevin Liptak contributed to this report.