US President Barack Obama and former President Bill Clinton attend a campaign event in New York

AFP

Bill Clinton campaigned with President Barack Obama, sprinkling political stardust on his Democratic successor and blasting challenger Mitt Romney for embracing the politics of "constant conflict."

The presumptive Republican nominee's campaign is using recent Clinton comments praising Romney's business record against Obama, but the ex-president left absolutely no doubt he was behind the Democrat.

"The alternative would be, in my opinion, calamitous, for our country and the world," Clinton warned.

Clinton, with Obama at his side, was speaking to some 50 Obama supporters who paid $40,000 each to attend a reception at the Manhattan home of hedge fund billionaire Marc Lasry, founder of Avenue Capital Group, reports AFP.

Clinton campaigned fiercely against Obama in 2008 when his wife sought, and barely lost, a historic battle for the Democratic nomination, but he has since mended fences with the president and is a trumpeter of Obama's economic policy -- even if he may at times stray off script.

But the husband of now-Secretary of State Hillary Clinton stayed fiercely on message at the first of the three Monday events, insisting the president has "good policies (and) a good record.

"He's made the best of a very challenging situation. He deserves to be re-elected," Clinton argued.

Romney and Republicans in Congress, Clinton said, "have adopted Europe's economic policy" of "austerity and unemployment," turning the tables on the common Romney campaign argument that Obama was embracing economic socialism akin to some governments across the Atlantic.

While Obama's policy is "job growth now, and long-term budget restraint," Republicans by contrast are focused on "wrongheaded" economics, Clinton said.

"The politics (are) wrong on the Republican side; the economics are crazy," he added.

Obama weighed in to say Republicans have abandoned the "basic consensus" that the market was the best generator of wealth, and that investments in infrastructure, education and the environment were critical.

Republicans "have run from a preference for market-based solutions to an absolutism when it comes to the marketplace, a belief that all regulations are bad, that government has no role to play," Obama said.

The 2012 election is more than anything about the US economy and jobs, and the coming months will see the parties clash over the role and size of government and how best to rein in runaway debt while fuelling economic growth.

The two presidents proceeded to a gala at the luxurious Waldorf Astoria hotel, where 500 guests paying at least $2,500 were to see a performance by rocker Jon Bon Jovi, according to the Obama campaign.

They capped off the fundraising with a Broadway concert, complete with stars like James Earl Jones and Mandy Patinkin, for about 1,700 people.

Obama will rake in at least $3.6 million for the evening, according to a campaign official.