Health-care politics apparently makes Democratic candidates say strange things when they are running for president. Remember in 2008 when candidates Barack Obama and Hillary Clinton were fighting over mandates?:

Enforcing a mandate will require some sort of penalty, such as fines, to ensure compliance, [Obama] said. “And that, I don’t think, is helping those without health insurance.”

I suspect the president recognized that mandates with penalties might be needed to ensure a viable risk pool, especially as he ensured they were ultimately built into Obamacare. But Clinton had a mandate, so he didn’t.

Eight years later, we have the spectacle of Clinton and her proxies attacking Sen. Bernie Sanders for pushing a single-payer health-care plan, arguing that his is a “risky” plan that will turn health care over to Republican governors. To be fair, this is partially the wonky Clinton criticizing the state’s role in Sanders’ plan (given the problems expanding Medicaid in some red states, she has a point). But Sanders legitimately shot back, “In 2008, she was attacking Obama because Obama was attacking her because she supported universal health care.”

Clinton later backed off, stressing, according to the Times, “that she was not faulting Mr. Sanders for supporting a single-payer plan, just for his lack of specificity.” That’s also fair, as Sanders recently released a scorecard showing the costs and pay-fors for his agenda, with one item missing: his plan for universal health care, by far his biggest-ticket item. “Tell the people how much it will cost them,” Clinton responded, surely thinking about the tax impact on middle-class households.

Okay, politics is messy, and I’ll leave it to others to sort that out. I can assure the Clinton team that there are many on the left who are turned off by attacks on Sanders’s progressive agenda from the right. But perhaps they’ve got a strategy here re centrists or something.

Like I said, not my department. Let’s instead talk about health-care policy and the broader politics therein.

At this stage in this election, I generally think it is too censorious to complain that a candidate’s idea won’t be able to get through Congress and, therefore, should not be raised. If that’s your criterion, there’s virtually nothing to talk about. Instead, candidates should do what they’re doing: sending signals to potential voters as to what they are about. Absent binding political constraints, how would they go after inequality, gender and racial inequities, taxes, market regulations, climate change and so on?

That they may not be able to do much of what they propose is, of course, important, and it’s fair to ask them how they will ultimately get their ideas through the gridlock. But for now, the electorate should learn about their policy differences without that constraint.

But health care is very different. Here, there’s a hard reality that should unite anyone who cares about affordable, universal coverage and lowering our uniquely high costs in this sector. And that is: After decades of fighting to get such a plan in place, Obama somehow managed to do so. The Affordable Care Act is the law of the land, and what I and I suspect many other progressives want to know is — how are you going to protect it from the marauding hordes that would destroy it?

Hold your fire, fellow progressives. I’ve been advocating for single payer since the late Ted Kennedy started talking about Medicare for All, long before a lot of you kids were born (“and while we’re at it, get off my lawn!”). And as a member of the Obama team back in the day, trust me, I know the Affordable Care Act has got some warts. But it exists, it’s working, it’s embedding itself in the lives of millions of households and, equally importantly, in the way we deliver health care.

So here I’ll firmly break my admonition that candidates ignore political constraints and insist that they spend about zero time fighting over single payer and instead tell us how they will build on this incredibly hard-won victory.

If Sanders disagrees and wants to push single payer, then Clinton is right: He should be upfront with how he will raise the trillions his single-payer plan will cost (net of the benefits to households of less expensive care). But from where I sit, that’s a distraction. I’m far more interested in what they will do to protect and improve the ACA.

In this regard, I give Clinton credit for putting forth a plan that builds on certain aspects of the health-care law. As it stands, the ACA requires most plans to provide free preventive services. She proposes to further hold down out-of-pocket costs by providing sick visits to low- and middle-income families that don’t count against deductibles. She proposes a refundable tax credit for excessive out-of-pocket costs, paid for by rebates from drug manufacturers and taxes on wealthy households. She wants the authority to “block or modify” unreasonable health plan rate increases and build on the ACA delivery system advances that promote quality of care over quantity of care.

On the other hand, Clinton has some explaining to do here, as well. One important tax supporting the ACA — the “Cadillac tax” — has been delayed and, I suspect, killed. Clinton opposed the tax and has pledged not to raise taxes on all but the top 3 percent of households, those with incomes exceeding $250,000. How is she going to make up for the loss of the Caddy tax? And while the ACA should be progressively funded, why should only those at the top of the scale pay for a national system of health care? What’s wrong with skin-in-the-game from less wealthy households?

Finally, let’s be clear about this next point: Sanders, a true progressive, supports the ACA and has fought as hard as anyone against attempts to repeal it. To some extent, he and Clinton are replaying the 2008 health-care-reform dance, sending differentiating signals to the base. That was great fun back in the day.

But those days are over. Somehow, the stars aligned and a barely functional federal government legislated a progressive, paid-for, universal-coverage health-care-reform plan that is reaching and helping people in every state in the union. As this election nears, it will be under increased threat by those who want to kill it. What I want to hear from candidates is how they are going to stop these forces.