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My Saturday began on the West lawn of Capitol Hill, where conservative activists were mounting one final, desperate effort to block health care reform. They came by the thousands, carrying flags and pushing strollers, in a demonstration of genuine grassroots fervor. They chanted “Kill the Bill,” over and over again, in a vaguely menacing tone that, perhaps, foretold a bit of ugliness to come.

But the most remarkable thing about the demonstration was how little it had to do with health care. The signs said “Stop socialism,” “A government of laws, not men,” “Respect our constitution--preserve our republic.” Nobody talked about death panels. Instead, one speaker--a Chicago radio host, I believe--attacked the First Lady’s obesity initiative. “Michelle, keep your hands off my kids’ lunchbox!” Yet another protest sign seemed to capture the mood perfectly: “This isn’t about health care. This is about control.”

A few hours later, inside the Capitol complex, President Obama urged House Democrats to do precisely what the protesters feared: Pass health care reform. It was not the first time he’d given such a speech. Just before the House voted on its initial reform bill in November, he’d come to Capitol Hill. And, broadly speaking, his intent had been the same: To embolden the Democrats by making them enthusiastic about the cause, demonstrating his own commitment to it, and making clear the political virtues of success.

But, like the protesters, this time Obama seemed to dwell less on health care and more on the significance of the moment. He invoked Lincoln, and the importance of fighting for principle. And then he invoked the legacy of the New Deal and Great Society, reminding members that their purpose in office was not to win elections--it was to make life better for their constituents. His closing argument was not about policy or politics. It was about posterity. And it was good.

For the last week or so, ever since it’s become apparent a climactic vote on health care was approaching, I’ve also been thinking about closing arguments. For most of the past year--and, really, it’s been far more than a year--the argument has been most practical. What would the bill do? What wouldn’t it do? And it’s easy enough to make the case for reform on those grounds.

As readers of this space know, I like to think of reform as achieving three broad goals: Making sure anybody can get an affordable insurance policy, shoring up everybody’s coverage so that it provides real economic security, and transforming medical care in order to make it both more effective and less expensive. Those arguments got a lot stronger this week, when the Congressional Budget Office determined that the final reform package--including both the Senate’s health care bill and the proposed amendments to it--would provide coverage to 32 million additional people, strengthen the baseline for coverage, and reduce the federal deficit over time.

But there’s another argument for health care reform, one that is at once more subtle and more sweeping. The disturbing part of our health care system is the financial and physical suffering it causes. But the unjust part of our health care system is the way it distributes that suffering. There are things all of us can do to stay healthy--we can eat right, we can exercise, we can avoid excessive risks. But even when we do the right things, we remain vulnerable.

You can have the perfect diet, jog three miles every day, and wake up one morning to discover you have cancer. So now you face mortal peril. And if, on top of everything else, you can’t pay your medical bills, you face financial ruin, as well.

Chance, of course, is part of life. Americans, in particular, seem to accept that. But every now and then, we have decided that need for such expansion--that there was, even now, the kind of common vulnerability to chance that required the sorts of initiatives we had enacted in the past. It happened with the New Deal, when we created the modern welfare state, and then again with the Great Society, when we expanded it.

The signature programs of these eras, Social Security and Medicare, work because they address a vulnerability we all share. Everybody is at risk of getting old; and everybody is at risk of misfortune, physical and financial, when that happens. To protect against that misfortune--to insure against that misfortune--all of us contribute. We all give, in the form of financial contributions; and we all get, in the form of financial security. Together, quite literally, we are stronger than when we are apart.

The conservatives protesting on the Capitol lawn Saturday see things differently. Health care reform isn't about contributing money for the sake of their own security; it's about having their money taken for the sake of somebody else's security. When they hear stories of people left bankrupt or sick because of uninsurance, they are more likely to see a lack of personal responsibility and virtue than a lack of good fortune. As my colleague Jonathan Chait has observed, theirs is an extreme version of a view common (although surely not universal) on the right: That individuals can fend for themselves, as long as they are responsible and as long as the government gets out of the way.

There's obviously a balance to be struck between these two world views. But, broadly speaking, conservative ideas about responsibility and vulnerability have dominated political discussion for most of the last four decades. That will change on Sunday, if health care reform passes. The bill before Congress may be flawed. And the process that produced it may be severely flawed. But it is, nevertheless, an expression of the idea that we--as as society--are not prepared to let people continue to suffer such dire consequences just because they’re unlucky.

A few hours after Obama was speaking, the Capitol had nearly cleared out. Leadership staff were meeting in House Speaker Pelosi's office while a few stray congressmen were giving floor speeches to a nearly empty chamber. By and large, though, members had scattered--a tell-tale sign that Pelosi was confident. If she'd still needed to do serious arm-twisting, she'd have held a series of votes to keep members on the Hill.

I walked the length of the building and then out to the east lawn where the conservative protesters, who spent the day visiting (and, on a few occasions, haranguing) House Democrats, had reconvened. The crowd was more subdued now. It was smaller, too--hundreds instead of thousands. The setting sun behind the capitol dome cast a long shadow over them, as night approached. But a new dawn would come soon enough. And with it, perhaps, a new era.