The big fight over health care is back on in the U.S. — and a lot of it will resonate in other rich nations grappling with the same cocktail of rising costs and human life spans.

Newly empowered Republicans in Congress this week introduced their plan to replace former President Barack Obama’s signature health care law, passed amid much pomp (Joe Biden called it a "big f---ing deal" in public) and partisan acrimony in 2010.

Though President Donald Trump campaigned to end the Obamacare “disaster” and the GOP runs Congress, much stands in their way. And when it comes to changing one of the cornerstones of American health care — a single payer, “socialized” health plan for the elderly — even the swamp-draining Trump has ruled out any tweaks, though as it is set up now, that system is unsustainable.

The U.S. debate holds multiple lessons for other countries, even if many Europeans view America's resistance to universal coverage and a leading role for the state in health with disdain.

Obamacare has never been particularly popular, but it’s never been more popular than now, as Republicans mount their first genuine threat.

But populist resentment, skepticism about big government and general fear of change when it comes to health care isn't unique to the U.S. Nor are the Americans alone in the developed world in struggling to come up with a workable alternative to an outdated and probably unaffordable health system.

Here are five things to watch for as the U.S. debate plays out in the coming months:

— “Nobody knew it could be so complicated," Trump marveled last week, explaining Republicans’ months of delay in producing a plan to replace the Affordable Care Act — which despite its problems has covered 20 million Americans and pushed the U.S. uninsured rate down below 10 percent (a record). The campaigners who worked to expand health coverage in America loathe the House Republicans’ proposed repeal of the mandate that individuals carry health insurance, their tax cuts and their scrapping of a major expansion of the social safety net (more on that later).

At the same time, Obamacare supporters are relishing some schadenfreude as they watch Republicans struggle to find a better way to help as many people for less money than the flawed Frankenstein monster of private insurance plans and public subsidies that is Obamacare. The ruling party can't seem to agree what the replacement plan should look like, or even if it should aspire to cover the same number of people. (Trump promised that no one now benefiting from Obamacare would lose coverage.)

— People hate the health status quo — until you try to change it. Obamacare has never been particularly popular, but it’s never been more popular than now, as Republicans mount their first genuine threat. According to a Kaiser Health Tracking poll conducted late last month, 48 percent of Americans approve of Obamacare, and 42 percent disapprove. It’s the highest level of favorability measured in 60 Kaiser surveys conducted since 2010, the year the law passed, and it's driven by independents’ softening views of the law. (Half of them now support it.)

Meanwhile, the vitriol Democrats faced in constituent meetings during the peak of the 2009 Obamacare debate is now being directed at Republicans, who have been drowned out in recent weeks by chanting protesters and impassioned pleas from people whose lives have been saved by the health law. Democrats suffered brutal political defeats in subsequent congressional elections amid the backlash to Obamacare. Now Republicans have to weigh the political costs of any change as well.

— The real fight to watch: Medicare. America’s most beloved health care program is arguably the closest to “socialized” medicine in the Bismarckian model. Medicare is a single-payer, government-run system that offers generous coverage to virtually everyone over 65.

Medicare, like other wealthy countries' universal coverage programs, is unsustainable. It was designed during an era when people died at age 70 of a heart attack, rather than living into their nineties with all kinds of chronic conditions that require steady and expensive care. To anyone following this social care crisis in, say, the U.K., this sounds all too familiar.

Most Americans don’t even realize how few people were covered under Medicaid, popularly understood as a health insurance program for the poor, prior to Obamacare.

The U.S. speaker of the House, Republican Paul Ryan, has long aspired to reform Medicare. His plan: Privatize it, with the government helping out with premiums rather than paying for everything, and raise the age of eligibility. That’s setting him up for a showdown with Trump, who has ruled out any changes to Medicare, which has long been known as a “third rail” of American politics.

Beleaguered French presidential hopeful François Fillon tried to poke at this in France, and got zapped. He proposed charging citizens more for routine illnesses so the Sécu, which is €160 billion in debt, could help manage expensive chronic ailments instead. There was immediate outcry — this was even before Penelopegate — and he had to backtrack severely. His health proposals now amount to free dentures.

In the Ryan-Trump Medicare face-off, the safe bet is on Trump.

— The biggest threat to Obama’s legacy — and to America’s move toward a public, universal health care system that might look familiar on the Continent — is the proposed rollback of Medicaid expansion.

Most Americans don’t even realize how few people were covered under Medicaid, popularly understood as a health insurance program for the poor, prior to Obamacare. In most states, especially those that voted for Trump, free medical coverage was only available to impoverished children and (maybe) their mothers. Poor single men who didn’t have a job, or couldn’t afford even sharing the cost with their employers, were basically out of luck.

That rhetoric carries echoes of the debate over welfare reform in the U.S. two decades ago, and carries racial undertones.

Obamacare tried to change that by making Medicaid available to everyone with a specific income near the poverty line. It was supposed to be mandatory, but after a U.S. Supreme Court setback gave each of the 50 states the option of expanding Medicaid, some Republican-controlled states resisted, despite the fact that the federal government paid for most of it. The fear of the freeloader, the able-bodied adult pocketing benefits at taxpayers' expense, is at the heart of conservatives’ objections to Medicaid and other parts of Obamacare. Just look at the provision in the Republicans’ latest proposal that would specifically bar lottery winners from qualifying for Medicaid. Or the comments Tuesday morning from key House Republican, Representative Jason Chaffetz of Utah, who said that “maybe rather than getting that new iPhone that they just love and they want to go spend hundreds of dollars on that, maybe they should invest in their own health care.”

That rhetoric carries echoes of the debate over welfare reform in the U.S. two decades ago, and carries racial undertones. (The so-called "welfare queen," a savvy matriarch who milks the system to live large, is implicitly a woman of color.) Ethnic tensions were stirred up in the 2016 election, in part by Trump’s anti-immigrant rhetoric that suggested outsiders are coming to take your benefits. It has parallels in European countries, whose health systems face new pressures from an influx of migrants. (Paging Marine Le Pen.)

— The longer you wait, the harder change is. The first Republican draft by no means signals the end is nigh for Obamacare, (despite the White House’s call for a bill to hit Trump’s desk in early April). Seventeen years passed between Hillary Clinton’s aborted 1993 health overhaul effort and the passage of Obamacare. Republicans spent seven years calling for a replacement before offering this opening gambit. Obamacare won’t be fading away anytime soon, and it’ll only get more and more entrenched.