During the election campaign, Barack Obama appealed to Martin Luther King's "fierce urgency of now" in support of his improbable candidacy. Now that Mr Obama is in office, voters are discovering what he meant by it.

Yesterday's 10-year budget document breaks pretty much every political rule in the book. By asking Congress to enact healthcare reform and a carbon cap and trade system within two years, Mr Obama is trying to pull off two feats that eluded his Democratic predecessors.

But the document is even more ambitious than that. By asking Congress to approve his core campaign promises at a time when the budget deficit has more than tripled in the space of a year to a post-second world war record and when the global financial system is in meltdown, Mr Obama is gambling that Americans will see this crisis the same way as he does - as an opportunity to remake the country.

"There are the years that come along once in a generation, when we look at where the country has been and recognise that we need a break from a troubled past, that the problems we face demand that we begin charting a new path," Mr Obama writes in the foreword to the 134-page document. "This is one of those years."

The next step will be to test the appetite for reform in Congress. John Boehner, the Republican leader in the House of Representatives, yesterday gave a flavour of the opposition verdict on Mr Obama's plans. "The era of big government is back," he said, "and Democrats want you to pay for it." The most ambitious element of the budget is the plan to adopt an economy-wide cap and trade system by 2012 in which the permits would be auctioned from the outset. The Senate defeated a less far-reaching cap and trade bill by a large margin last year. Mr Obama is betting that the combination of global crisis and new leadership has drastically changed the political climate.

"President Obama is declaring that the age of incrementalism is dead and that he can pull off all his priorities at the same time," says Bill Galston, who was a senior official in Bill Clinton's White House. "Having ignored everyone's advice not to run for the presidency because he couldn't win and then proved them wrong, he is now taking the same approach to governing. It is breathtaking in its -ambitions."

The second audacious -element in the document is his plan to enact universal health insurance while also reducing long-term health costs. Either of these -objectives would be a steep climb under normal circumstances.

But by creating a 10-year $634bn reserve fund of savings to pay for healthcare reform - a kind of honey pot to bring in sceptical fiscal conservatives - Mr Obama is again betting that he can change the nature of the conversation.

It reverses Mr Clinton's failed 1993 attempt at healthcare reform in which he delivered a detailed policy blueprint to Congress without the money to pay for it. Mr Obama has kept the policy details open for negotiation. Again, the new president is placing a large bet on his powers of persuasion.

"It's a rule of politics that when the window of opportunity is open you jump through it," says Jim Lindsay, a politics professor at the University of Texas. "President Obama is using the power of the bully pulpit and the opportunity of a crisis to try to change the rules of the game."

There are other, farreaching elements in the budget, including a dramatic expansion of federal funding for education, scientific research and infrastructure. And there is the pledge to halve the deficit he inherited from George W. Bush by the end of his first term.