The historic importance of Barack Obama's presidency doubled this weekend. The House of Congress' approval for comprehensive healthcare reform is on the same plane of significance as the election of the United States' first African-American President 16 months ago.

The bill is of vast symbolic importance for a country which had been trying to enshrine the principle of universal healthcare coverage in law for almost half a century. But this symbolic magnitude is more than matched by the substance of the bill, which will extend insurance coverage to 32 million presently uncovered Americans and ban discrimination by insurance companies against those with pre-existing medical conditions.

The legislation is far from perfect. The absence of a "public option" health insurer means there is still scope for abuse from private insurance companies and other powerful vested interests in the system. But the bill does, as President Obama stressed on Sunday night, move things in the right direction.

This is, to a large extent, a personal achievement for the President. After the shock loss of Ted Kennedy's Massachusetts Senate seat to the Republicans in January, many around the President urged him to drop healthcare reform and concentrate on the economy. He rejected that advice and instead staked his presidency on getting the bill through. Mr Obama would have been fatally weakened if he had failed. Instead, he emerges strengthened from the ordeal. Mr Obama has shown that he is more than just a fancy orator; he can get things done too.

But an even tougher battle now looms: selling the bill to a sceptical American public. There is widespread hostility to the bill and the Democrats are facing heavy losses in November's mid-term Congressional elections. Democrats – led by the White House – need to campaign fiercely and to make the case for the bill they have forced through the legislature. This means explaining its merits to the public, something that they have, until recently, failed to do.

The good news is that they have a powerful message to sell. Many Americans are opposed to the bill because they are concerned about its cost implications. They are understandably nervous of new public spending commitments at a time of record government deficits. But the reality is that this legislation will bring deficits down over time by reducing bills for Medicare and Medicaid (existing government health programmes for the elderly and poor). One effect is that if people get good care sooner, they are less likely to need expensive treatment, at public expense, later in life.

Another potent public fear is of the "socialisation" of medical care. But America has been here before. Medicare faced significant opposition when it was introduced 45 years ago on the very same ideological grounds. But now those attacking "Obamacare", including Republican legislators, cherish Medicare because they know it is popular with the public. The lesson is that it is a mistake to presume that public opinion is fixed in stone.

This is not to argue that the fight ahead for Mr Obama and the Democrats will not be terribly difficult. But reason – if allied to political will and action – can still prevail. What this weekend's victory shows is that successful political leaders are prepared to show some audacity when the time is right; the audacity of hope, as someone once put it.