His remarks in a speech yesterday to the Financial Services Council in Sydney were aimed directly at the core support base of the man who might soon be running the world's sole superpower and Australia's most important ally.
While unlikely to damage the two countries' alliance, a resentful Romney Administration could rebound on Labor as it struggles to win back sufficient support to remain in power at next year's election.
Polls show Australians overwhelmingly support the US alliance, and much of Swan's message of economic success in the face of global diversity yesterday has been eclipsed by "Republican cranks and crazies" headlines.
New Morgan polling shows that 60 per cent of Australians do not trust the Government - twice the 2009 level, when ousted Prime Minister Kevin Rudd was in office - and only one in three believes Labor is doing a good job.
The Opposition immediately attacked Swan in a bid to regain momentum lost as Prime Minister Gillard has pushed ahead with her agenda and risen in the polls.
Opposition leader Tony Abbott said the Treasurer should concentrate on lifting his own performance rather than criticising others, and shadow treasurer Joe Hockey said Swan loved hating people.
"He hates Tony Abbott, he hates [mining magnate] Gina Rinehart, he hates Twiggy Forrest, and he hates the Republicans," Hockey said.
Swan had his own tale of success, citing Australia's AAA rating by the three major global ratings agencies, International Monetary Fund predictions of continued strong growth, and 21 consecutive years of expansion.
"Our economy is now 11 per cent bigger than at the end of 2007 [when Labor won power]," he said.
But Swan said that in the US the national interest had been held hostage by the extreme right Tea Party wing of the Republic Party.
"There can be few things more alarming in public policy than a political movement which was genuinely prepared to see the US Government default on it obligations in order to score a political point.
"Fast forward to today, against the backdrop of a very close presidential campaign, and global investors are once again keenly focused on political gridlock in the US."
Swan said the resulting "fiscal cliff" of legislated spending cuts and tax increases due next year was 5.1 per cent of gross domestic product.
"This would tip the US back into recession," he said.
"Let's be blunt and acknowledge the biggest threat to the world's biggest economy are the cranks and crazies that have taken over a part of the Republican Party."
Swan also criticised the European Union, accusing its leaders of lacking the political courage required to take hard decisions for long-term benefits, comparing them unfavourably with Labor's record.
"Here in Australia we have a rich and proud history of leaders who have set aside their political interests to take decisions in the long-term national interest ...
"We've stumped up and pushed forward when the times called for it. Europe has much of this nation building task still ahead of it."
