O.K., folks, this is it. It’s the defining moment for health care reform.O.K., folks, this is it. It’s the defining moment for health care reform.

Past efforts to give Americans what citizens of every other advanced nation already have — guaranteed access to essential care — have ended not with a bang, but with a whimper, usually dying in committee without ever making it to a vote.

But this time, broadly similar health-care bills have made it through multiple committees in both houses of Congress. And on Thursday, Nancy Pelosi, the speaker of the House, unveiled the legislation that she will send to the House floor, where it will almost surely pass. It’s not a perfect bill, by a long shot, but it’s a much stronger bill than almost anyone expected to emerge even a few weeks ago. And it would lead to near-universal coverage.

As a result, everyone in the political class — by which I mean politicians, people in the news media, and so on, basically whoever is in a position to influence the final stage of this legislative marathon — now has to make a choice. The seemingly impossible dream of fundamental health reform is just a few steps away from becoming reality, and each player has to decide whether he or she is going to help it across the finish line or stand in its way.

For conservatives, of course, it’s an easy decision: They don’t want Americans to have universal coverage, and they don’t want President Obama to succeed.

For progressives, it’s a slightly more difficult decision: They want universal care, and they want the president to succeed — but the proposed legislation falls far short of their ideal. There are still some reform advocates who won’t accept anything short of a full transition to Medicare for all as opposed to a hybrid, compromise system that relies heavily on private insurers. And even those who have reconciled themselves to the political realities are disappointed that the bill doesn’t include a “strong” public option, with payment rates linked to those set by Medicare.

But the bill does include a “medium-strength” public option, in which the public plan would negotiate payment rates — defying the predictions of pundits who have repeatedly declared any kind of public-option plan dead. It also includes more generous subsidies than expected, making it easier for lower-income families to afford coverage. And according to Congressional Budget Office estimates, almost everyone — 96 percent of legal residents too young to receive Medicare — would get health insurance.

So should progressives get behind this plan? Yes. And they probably will.

The people who really have to make up their minds, then, are those in between, the self-proclaimed centrists.

The odd thing about this group is that while its members are clearly uncomfortable with the idea of passing health care reform, they’re having a hard time explaining exactly what their problem is. Or to be more precise and less polite, they have been attacking proposed legislation for doing things it doesn’t and for not doing things it does.

Thus, Senator Joseph Lieberman of Connecticut says, “I want to be able to vote for a health bill, but my top concern is the deficit.” That would be a serious objection to the proposals currently on the table if they would, in fact, increase the deficit. But they wouldn’t, at least according to the Congressional Budget Office, which estimates that the House bill, in particular, would actually reduce the deficit by $100 billion over the next decade.

Or consider the remarkable exchange that took place this week between Peter Orszag, the White House budget director, and Fred Hiatt, The Washington Post’s opinion editor. Mr. Hiatt had criticized Congress for not taking what he considers the necessary steps to control health-care costs — namely, taxing high-cost insurance plans and establishing an independent Medicare commission. Writing on the budget office blog — yes, there is one, and it’s essential reading — Mr. Orszag pointed out, not too gently, that the Senate Finance Committee’s bill actually includes both of the allegedly missing measures.

I won’t try to psychoanalyze the “naysayers,” as Mr. Orszag describes them. I’d just urge them to take a good hard look in the mirror. If they really want to align themselves with the hard-line conservatives, if they just want to kill health reform, so be it. But they shouldn’t hide behind claims that they really, truly would support health care reform if only it were better designed.

For this is the moment of truth. The political environment is as favorable for reform as it’s likely to get. The legislation on the table isn’t perfect, but it’s as good as anyone could reasonably have expected. History is about to be made — and everyone has to decide which side they’re on.