President Obama referred to his challenger Mitt Romney as a "bullsh**ter" in an interview with Rolling Stone magazine, the latest salvo in a campaign that has seen its share of insults hurled from both sides.

Passed on a message from the young daughter of an editor of the magazine, the president remarked that he "does very in that demographic. Ages six to 12? I'm a killer … You know, kids have good instincts. They look at the other guy and say, 'Well, that's a bullsh**ter, I can tell.'"

Romney campaign spokesman Kevin Madden responded, saying, "President Obama is rattled and on the defensive. He's running on empty and has nothing left but attacks and insults. It's unfortunate he has to close the final days of the campaign this way."

In truth, both campaigns and their allies have hurled insults and insinuations at one another, with charges ranging from the commission of possible felonies to possibly having a hand in a woman's death to the unconstitutional assumption of the presidency by a noncitizen. A week ago, Romney's son Tagg told a radio interviewer that he felt like running down to the stage and taking a swing at the president during the second presidential debate, a comment he apologized for at the end of the third debate.

When asked about the president's "bulls***er" comment, White House communications director Dan Pfeiffer said he hadn't yet read the article but argued, "What is true is that trust is very important in this election. The president is someone who says what he means and does what he says." He suggested reporters shouldn't be "distracted by the word" bullsh**ter but should be focused on the larger issue of Romney's trustworthiness.

Pfeiffer cited the myriad shifts in positions Romney has made, including whether or not he would seek a tax cut for the top 1 percent, which he once proclaimed he would do but now says would be offset by the elimination of tax deductions and loopholes for the wealthy.

Questioning Romney's honesty and trustworthiness is indeed is one of the president's main messages on the campaign trail, with the Obama campaign convinced that the president's advantage in whom voters perceive as trustworthy will help sway undecided voters. Knowing of the ambivalence many voters feel about the job the president has done, part of the president's strategy has been to paint Romney as an unacceptable alternative.

In Tampa, Fla., this morning, the president charged that Romney "knows his plan isn't any different than the policies that got us into the mess. So in the final weeks of this election, he's counting on you forgetting that his policies aren't going to work. He's hoping that you won't remember and you'll come down with a case of what we call Romnesia."

After saying that Romney's plan "is likely to create jobs in China, not America," and that "he wants to give millionaires and billionaires a $250,000 tax cut," which will either increase the deficit or force tax increases on middle-class families - charges the Romney camp denies - the president asserted that Romney is "hoping you're going to come down with a severe case of Romnesia just before you cast your ballot."

And lest anyone think Romnesia was merely a fun play on words, the president said, "now, Tampa, we joke about Romnesia, but all of this speaks to something that's really important in this election and that is the issue of trust. When you elect a president, you're counting on somebody you can trust to fight for you, who you can trust to do what they say they're going to do, who can trust - that you can trust to make sure that when something unexpected happens, he or she is going to be thinking about your families, your future. Trust matters."

The pitch comes at the same time the president laments the onslaught of negative TV ads that flooding the airwaves in battleground states. "You've now seen three debates, months of campaign events, and way too many TV commercials," Obama said at a rally today in Richmond, Va.

But lamentations aside, new data from an independent report show that Obama and his allies are responsible for the majority of ads - and the most negative ads - in the final stretch of the campaign. While Republican groups and presidential nominee Mitt Romney have spent $10 million more than Obama on ads this month, it's the president who has actually put more spots on the air - 15,000 more than his rival, according to the Wesleyan Media Project, which tracks media buys.

Wesleyan found that President Obama's campaign has been much more negative, despite his rhetoric on the campaign trail decrying the nasty attacks. The study found nearly three-quarters of pro-Obama ads in October - 73.3 percent - were negative attacks on Romney. Twenty percent emphasized contrasts between the candidates, while 6 percent were positive, the study found. By contrast, Romney and his allies have been modestly more positive, with nearly 12 percent of ads refraining from contrasts or attacks. Thirty-six percent of pro-Romney ads this month have been negative attacks

- Jake Tapper, Devin Dwyer and Mary Bruce