Iowa's Republican presidential contest is bringing out harsh attack ads from supporters of Rick Perry (left) and from Ron Paul's campaign. Photograph: Mario Anzuoni/Reuters

A tide is flowing through American politics: a tide of money unleashed by a supreme court decision that opened the floodgates to unlimited spending on advertising by so-called "super pacs" – political action committees loosely affiliated with individual candidates.

Iowa, site of the coming Republican presidential caucuses, is the first state to see the effects of the new political landscape, as duelling GOP candidates pummel each other with a cascade of negative advertising costing millions of dollars and filling the airwaves.

Turn on a television in Davenport or Cedar Rapids this week and you won't be able to miss the doom-laden advertising spots aimed at damning one or another of the Republican presidential candidates or even "the liberal Republican establishment".

But rather than ending with the now familiar "I'm Candidate X and I approve this message," these new super pac-funded ads finish with the words: "Super pac Z is responsible for the content of this message."

The arms-length relationship between the super pacs and the individual candidate's campaigns – which under election law cannot co-ordinate campaign spending or activities – allows candidates such as Mitt Romney or Newt Gingrich to disclaim any influence over the sources of the ads, in effect allowing the super pacs to throw mud while allowing the candidate to keep his or her hands clean.

The big-spending Ron Paul has no such worries, with Paul funding and supporting some of the most savage advertising aimed at both Gingrich and Romney. The Des Moines Register reported that the Paul campaign plans a $10m ad blitz in Iowa and New Hampshire for the final days.

Figures collected by the Des Moines Register show that super pacs affiliated to just two campaigns – those of Romney and Rick Perry – have spent more than $4m on television ads in Iowa alone in December.

That's on top of the more than $8m according to some estimates that will be spent this month by the official campaigns.

Some of the new breed of ads have been positive, extolling the virtues of the candidate that the super pac backs. But as the race has gotten increasingly heated, the ads have become more negative, and in some cases barely within the bounds of fact.

• Restore Our Future: super pac supporting Mitt Romney

While the official Romney campaign has spent $1.2m on TV advertising in Iowa, the Restore Our Future super pac has spent $2.85m, largely on negative advertising attacking Newt Gingrich – including this brutal ad above.

• Make Us Great Again: super pac supporting Rick Perry

While the Perry campaign is rumoured to be spending as much as $4m on advertising in Iowa this month and January, the affiliated Make Us Great Again super pac is chipping in another $1.3m, including this mock newsreel attack ad aimed at Gingrich and Romney.

• Ron Paul presidential campaign committee

Ron Paul's campaign has directly funded a mix of positive and negative campaign ads, spending upwards of $1.3m this month in Iowa – including this negative ad accusing Gingrich of serial hypocrisy.

The new super pacs are the result of a supreme court decision in 2010, the "Citizens United" ruling that blew a hole in existing campaign spending laws. Under Citizens United, the court ruled that the right to freedom of speech allowed under the constitution forbade restrictions on political advertising funded by corporate donations.

That ruling led to the formation of political action committees dubbed super pacs, officially known as "independent-expenditure only committees," which can raise unlimited sums from corporations, unions and other groups, as well as from individuals.

The airwaves of Iowa aren't alone in being flooded with political ads. Super pac advertising is also being screened in New Hampshire, South Carolina and Florida, and the amounts are sure to increase as the primaries in those states get closer.

The Republican primaries are just a warm up for the main event. The big money is waiting for the start of the general election campaign in the summer and autumn of 2012, as Democrats and Republicans approach the general election, with control of the White House and the Senate at stake. Stay tuned – or just turn on a TV set.