He contrasted the Republican challenger's austere budget plans with Barack Obama's stimulus-orientated response to the 2008 financial crisis.
Electing Mitt Romney to the White House this November would be "calamitous" for America and the world, according to the former president Bill Clinton.
He contrasted the Republican challenger's austere budget plans with Barack Obama's stimulus-orientated response to the 2008 financial crisis that saved the car industry in the United States.
Clinton said his Democratic successor deserved a second term in the White House because of his record in stewarding the economy through a "miserable situation", and "the alternative would be, in my opinion, calamitous for our country and the world".
The former president's intervention during a whistle-stop round of fund-raising events in New York came as both campaigns intensified their attacks on each other's records as job creators while in office.
Clinton and Obama were accompanied on Air Force One by the rock star Jon Bon Jovi who performed an acoustic version of his anthem Living on a Prayer for guests at the Waldorf Astoria.
It was one of three events held on Monday which raised an estimated $3.6?million [pounds 2.3?million] for the Obama campaign.
Reports from the event at the Manhattan home of Marc Lasry, a billionaire hedge fund founder, said Obama and Clinton put on a relaxed and friendly double act, showing no trace of the animosity from the long and bitter 2008 campaign in which Obama defeated Hillary Clinton for the Democratic nomination.
Clinton's attack appeared to atone for his remark last week that Romney had a "sterling" business record.
The verdict was unhelpful to the Obama campaign, which has tried to paint the former boss of Bain Capital, a management consultancy, as a rapacious "vulture" capitalist.
Clinton said that Republican plans to slash public spending endorsed by Mitt Romney, were "wrong-headed" and would lead to more pain for ordinary Americans.
"What they're talking about is something that is fundamentally different from our experience in growing this economy and creating jobs," he said.
"And so that's going to be the central issue in this campaign. And we're going to do everything we can to clarify that choice."
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