Thanks to the health-care law that brought much of the U.S. government to a grinding halt this week, Alex Parkinson is no longer uninsurable.

The Portland, Ore. resident and chief technical officer at a local start-up had previously tried to buy health insurance but was denied coverage because he has Crohn's disease, a pre-existing condition that effectively forced him to join the ranks of America's roughly 48 million uninsured residents.

"They make you fill out a form and it includes questions about your medical history," Mr. Parkinson said. "That's just how it goes."

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But since the Patient Protection and Affordable Care Act – dubbed Obamacare – came into effect this week, pre-existing conditions can no longer be used to deny health-insurance coverage. The change represents part of a profound overhaul of the U.S. health-care system, long criticized as one of the least cost-efficient in the developed world. It has also become one of the most contentious issues in modern American politics, so unpalatable to its opponents that the Republican-controlled Congress this week opted not to agree on a new budget – effectively shutting down the federal government – unless the new health-care law is significantly changed, postponed or repealed altogether.

"The fact is the word 'socialism' has a huge stigma for half the country," said Mr. Parkinson, who intends to purchase insurance this week. "[The health-care law has] been a pretty divisive, polarizing issue.

"It's something that doesn't make any sense to me."

On Wednesday, as the government closure entered its second day, officials from a vast array of federal, state and municipal offices began to brace for the devastating effects of a prolonged shutdown. At the same time, millions of people got their first real look at how the law at the centre of the government shutdown actually works in practice, as the doors opened on health plans that are now mandated for uninsured Americans.

In almost all respects, the Affordable Care Act is far less comprehensive than the single-payer, universal systems available in countries such as Canada. Under the law, virtually all Americans who don't already have health insurance must get some kind of coverage or face a fine. Starting this month, Americans can sign up for a plan using state-by-state health-care "exchanges," which act as marketplaces, letting users choose from a variety of plans. Applicants can no longer be denied coverage based on their medical histories, and certain applicants can qualify for partial or total subsidies based on their income levels.

The plans vary widely based on how comprehensive they are – ranging from "Platinum" plans, which have high monthly fees but fewer out-of-pocket expenses, to "Catastrophic" plans, which require a user to pay all medical costs up to a certain amount, usually in the thousands of dollars.

So far, the law has still been the source of deep uncertainty for many Americans. A September poll by the Henry J. Kaiser Family Foundation found 51 per cent of respondents said they did not have enough information about the act – primarily, how much it will cost and who will foot the bill.

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As a result of the ongoing confusion, some of the state-based health-care exchanges have, in the past months, spent tens of millions of dollars on radio, newspaper and other ads touting the new law. Hoping to generate public goodwill, the Oregon exchange, Cover Oregon, has paid for billboards and other ads that associate the new entity with the state's outdoor lifestyle.

But while the ads may have raised awareness about the exchanges themselves, they appear to have done little to sway opinion about the health-care law. The Kaiser poll found approval of the Affordable Care Act split neatly down party lines, with two-thirds of Democrats and only one-third of Republicans in favour.

The polarization has done little to raise hopes for a quick end to the government shutdown prompted by Republican distaste for the law.

Across the United States, signs of a stalled federal government are mounting. More than 400 national parks – including iconic tourist destinations such as Yosemite and Yellowstone – are closed to visitors. Some national forests, which dominate much of the landscape in states such as Oregon, are partially accessible, but their ranger stations sit empty.

Virtually every federal department has sent home some or most of its employees. In some cases, such as that of NASA, all but a tiny fraction of workers have been deemed essential enough to remain on the job. The shutdown's impact is most readily visible in Washington, D.C., where many of the 800,000 or so furloughed federal employees work and where well-known sites such as the Lincoln Memorial are now closed for the indefinite future.

But for most states in the country, the most profound effects of the federal government shutdown are indirect ones – and almost all of them relate to funding.

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A massive swath of state-administered programs are funded in part by money from Washington – these include programs such as food stamps and financial assistance for those living at or near poverty levels. Should the shutdown continue for more than a couple of weeks or so, those programs could be the first to see serious cuts.

"The biggest issue for us is a cash-flow issue right now," said Matt Shelby, spokesman for the Oregon Department of Administrative Services. "If we get a few weeks into a shutdown, we'll need to get more specific about certain programs and their funding.

"We've had assurances from the federal government that money will continue to flow, but we're not sure."