By Paul Krugman.

President Obama will give his big health-care speech tomorrow. Let’s hope he does it right.

What does that mean? It means not playing professor; it means not having the speech read as if it were written by a committee (like that woefully weak op-ed in the Times a couple of weeks back); it means showing real passion about health care, which has been sadly lacking so far.

I, for one, won’t be obsessing about exactly which pieces of proposed reform he emphasizes — because that’s not what’s driving the politics. Americans haven’t become skeptical about Obamacare because they’d rather shave an extra $30 billion a year off the cost; they have not, contrary to “centrist” fantasies, been turned off by the details of the stimulus plan or cap-and-trade. What has been missing is a vision. And this is probably the last chance to supply that vision.

So what should Obama do? I am not a speechwriter, but here’s my view:

1. Make it personal: In general, I’m not big on the personal anecdotes. But right now, Obama really needs to make it clear that the horrors of our health care system can lead to nightmarish outcomes — and that those nightmares can happen to you, or someone like you. This is the time for “Lois Lane, of Smallville, Kansas, lost her coverage when her employer went bankrupt. When she tried to get individual coverage, she was turned down because she once had a rash in college. Then she got cancer …”

2. Talk about Medicare: Incredibly, the Obama administration has let conservatives — conservatives! — position themselves as the defenders of Medicare. Obama needs to remind viewers that Medicare was a deeply controversial program, that there were dire warnings about what the program would do, and that the people who tried to prevent the creation of Medicare (and keep trying to dismantle it) are the very same people now opposing health-care reform. Talk about how many Republicans voted for a resolution calling for Medicare privatization just months ago!

3. Talk about the system’s troubles: Obama really needs to convey the urgency of reform; he should talk about the doubling of premiums over the past decade and, crucially, the way ever fewer employers are offering coverage. The message should be, even if you think your insurance is OK now, it could well be gone in a few years.

4. Explain the plan in as few words as possible: Here’s my stab at it — one hopes the speechwriters can do better, but it gets at the essence. “We’re going to make sure that every American has access to the same insurance deals big employers get. We’re going make sure that no American can be denied coverage at a reasonable rate because of previous medical history. And for those Americans who find it hard to afford essential insurance, we’ll provide financial aid.

“Now, there are a few things we’ll need to do to make this work. We’ll have to require that all large employers either offer coverage to their workers or pay into a fund that helps them get their own insurance. We’ll sign people up for insurance now, even if they’re healthy, because it’s not fair to others if you wait until you’re sick to join the system. And we’ll keep the insurance companies honest by offering people the choice of buying their insurance directly from a public plan.

“Let me be honest: this won’t come free. But this plan will give Americans the fundamental security of knowing that for the rest of their lives they and their families will have the health insurance they need, insurance that they can’t lose.”

That’s the main thrust.

Oh, and about the public option: yes, it should be in the speech — and not just because it will lower costs. From personal discussions I know that the individual mandate really gets peoples’ hackles up,because they see it as a giveaway to the insurance industry (you may recall that many Obama supporters made precisely that case during the primary). Yet the individual mandate is necessary — so it’s crucial to have the counter-argument that look, people can choose the public option. Yes, some senators will fight against that option tooth and nail — but that’s for later.

What I hope Obama realizes is that this speech should not be aimed at Kent Conrad or Susan Collins. A national address is not where you do your backroom deals. This speech has to be aimed at regaining the trust of the American people. It needs to be something with vision and sweep, not an item-by-item detailing of what the administration is prepared to concede.

This is a time for Obama to show real leadership — not to uplift the nation with vague generalities, not to sound like a technocrat, but to persuade America that it needs to change. Can he do it? Let’s see.