The crush of presidential campaign ads is here. Less than five weeks before voting begins in the 2012 presidential contest, the Republican candidates are stepping up their presence over the TV airwaves and online. Super PACs have been running ads, and the Democratic National Committee is doing its best to try to weaken a leading GOP contender, former Massachusetts Gov. Mitt Romney.

President Barack Obama has even tiptoed into the fray with a limited ad buy soliciting volunteers for his campaign. "We've been waiting for it to start, and it's been a little slower in Iowa and New Hampshire than we expected. But that doesn't say anything about what's going to happen next, and in the coming year," said Ken Goldstein, president of the Campaign Media Analysis Group, which tracks ad spending.

The new, more aggressive advertising phase comes as the Republican field remains deeply unsettled before the Iowa caucuses Jan. 3. The New Hampshire primary follows on Jan. 10.

The field may become more volatile still. After months of training their attacks primarily on Obama, a Democrat seeking his second term, the Republicans are beginning to assail one another.

This emerging ad crush poses particular challenges for Romney, who polls at or near the top of the field in the early states but has failed to consolidate support behind his candidacy. While he's tried to run a general election strategy focused on beating Obama, he's been the target of attacks from both his GOP rivals and the DNC.

Romney's campaign began running its first TV ad just last week, in New Hampshire, and it immediately drew criticism. The ad criticizes Obama's handling of the economy and appears to quote the president from the 2008 campaign saying, "If we keep talking about the economy, we're going to lose." But the quote is misleading -- Obama was paraphrasing a comment from an aide to then-Republican rival John McCain. Romney has stood by the ad, saying the quote is fair game.

Romney's campaign announced Thursday it would begin running ads in Iowa, signaling he has decided to compete fully in the state after steering clear of it for much of the campaign. Romney spent about $10 million in Iowa in 2008 only to lose the caucuses to former Arkansas Gov. Mike Huckabee.

Romney's rivals, meanwhile, have sharpened their attacks on him. Texas Gov. Rick Perry released a new ad Friday in Iowa that gently knocks Romney. "I'm not ashamed to talk about my faith," Perry says in the ad -- a contrast to Romney, who has refrained from much discussion of his Mormon belief on the campaign. Many Republicans who participate in the Iowa caucuses are evangelical Christians, some of whom regard Mormonism with suspicion.

Former Utah Gov. Jon Huntsman has launched a tough Web ad against Romney, using a tense interview Romney gave with Fox News earlier this week as a pretext to renew criticism of the former Massachusetts governor as a flip-flopper on key issues. Our Destiny, a super PAC supporting Huntsman, has spent $650,000 on an ad in New Hampshire indirectly hitting Romney. Huntsman, the ad promises, won't be a "phony who tells me one thing and you another."

The DNC has also gotten in the game, producing a TV spot likening Romney's shifting positions to "two men trapped in one body." The ad is being aired in a handful of swing states, and it garnered considerable publicity in national news outlets.

But Romney isn't the only target. Former House Speaker Newt Gingrich, who has surged to the top of many recent polls, has come under withering attack from rival Ron Paul. The Texas congressman released a scathing Web video painting Gingrich as a shape-shifting mercenary who has changed position on key issues because of lucrative consulting contracts with the housing giant Freddie Mac, the health care industry and others.

Romney gently pokes Gingrich in his new Iowa ad, which closes with a shot of Romney and his wife of 42 years, Ann, walking through a corn field and holding hands. It's a not-so-subtle contrast with Gingrich, who has been married three times and has acknowledged infidelity in his first two marriages.

Gingrich hasn't aired commercials yet but his rising popularity has fueled a burst of fundraising success that could pay for some advertising in the coming weeks, campaign officials said.

Perry has devoted more resources to TV advertising than anyone in the field. His campaign took the unusual step of buying ads on the national Fox News Network, an expensive gamble aimed at boosting his credibility with conservatives following several weak debate performances. The campaign has also spent more than $2 million on television in Iowa, including a special "one-time only" ad making light of Perry's recent flub of which Cabinet departments he'd eliminate. The ad was paired with Perry's appearance Thursday on NBC's "The Tonight Show."

A pro-Perry super PAC, Make Us Great Again, has spent nearly $900,000 to run ads in Iowa, New Hampshire and South Carolina, another early voting state.

The ad blitz hasn't done much to boost Perry's standing in the race. Most polls show him trailing many rivals in the early states, including Romney, Gingrich, Paul and businessman Herman Cain.

Cain, who briefly topped many polls until he was hit with sexual harassment allegations last month, released a new ad promoting his business credentials Thursday in part to insist his campaign remains on track. But it's unclear whether the ad is actually airing anywhere. A Georgia woman came forward this week claiming to have had a 13-year affair with Cain, and while he has denied the allegations, he has said campaign contributions have dried up and he's reassessing whether to stay in the race.

Obama, meanwhile, has appeared in two new re-election ads urging people to volunteer for his campaign. "Don't sit this one out," the president says, apparently trying to counter the expectation that the intense grassroots interest in his candidacy in 2008 has abated this time. Campaign aides said the ad is airing lightly on satellite television and only as a test to see whether TV is an effective way to recruit volunteers.

(Copyright 2011 by The Associated Press. All Rights Reserved.)

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