Leading article: A victory that may come to define the Obama presidency

American presidents, it is often said, have about a year to make their mark – enact a major piece of legislation that then shapes and defines the rest of their term in office. Failure to choose the right weapons, or the right turf, can be fatal.

Barack Obama has at times struggled to find a cause he can truly make his own. He seemed to take on too many issues at once, from Middle Eastern peace to climate change, without demonstrating that he had a clear strategy to carry them through. With the Senate's passage of his bitterly contested healthcare bill, the clouds have lifted a little. Just in time for the Christmas break, the President can afford to wipe the sweat from his brow and contemplate his holiday with some satisfaction.

Much attention here and in the United States has been focused on what this mammoth undertaking, involving nine months of political haggling, has already cost him politically. To many of the most fervent Obama supporters, the compromises he has had to strike in order to guide the bill through the Senate and the House of Representatives have resulted not in a golden mean but leaden mediocrity. For left-wing Democrats, abandonment of the so-called public option, the direct provision by the state of health insurance for the poor, is a bitter pill.

That is almost certainly a lost cause now, a casualty of a savage Senate battle against resurgent Republicans who closed ranks against Obama's supposedly "socialist" health reforms with frantic and, at times, disconcerting zeal.

Nor is the battle over the trimmed-down health reform package finished, even now. What the Senate agreed to on Christmas Eve was not the same package that the House of Representatives nodded through in the autumn. A joint committee will have to meet, therefore, probably within the next few days, to fuse the two bills into one, which will then go back to both houses. Only then will the bill become law, hopefully before the President delivers the State of the Union address next month.

Nevertheless, we should not lose ourselves in all the details about messy compromises, and so miss the vital significance of what Mr Obama is tantalisingly close to achieving. The President is surely right to assert that most of a loaf is better than no loaf at all, and to describe his health reform package as the most important item of social policy in America since the 1930s.

Tens of millions of poor Americans who have been denied healthcare cover in the past can in all likelihood look forward quite soon to a day when they will be able to face the prospect of illness with a little more equanimity than they do now. Under the new bill, most people who are not currently covered by Medicaid – the existing federal and state-funded insurance scheme for those on low incomes – will either have access to it, or will receive subsidies to obtain health insurance elsewhere. Businesses will be obliged to offer coverage to their employees. The number of potential beneficiaries of these changes is huge, and could affect the lives of more than 30 million people.

Democratic presidents and politicians since the era of Teddy Roosevelt have fought and lost battles to set up a comprehensive national system of health insurance for Americans – a system that would benefit the many, not just the few. The Clintons tried their hand at this and failed. If Mr Obama closes this deal, he has a chance to earn a place in American history as a great reformer.