Coronavirus: As cases reach 4 million, why is the virus spreading so fast across the US?

New coronavirus cases in the US have more than doubled within the last months, pushing the confirmed number of nationwide infections to more than 4 million.

The US reached its first 2 million confirmed cases on 11 June, entering a fourth month of a pandemic that has shown no signs of relief despite immense federal pressure to resume American life amid mass unemployment, growing unrest against police violence and looming evictions that could threaten millions of Americans. More than 3 million cases were identified by 7 July.

Less than three weeks later, nationwide infections have surpassed 4 million, according to Johns Hopkins University. More than 143,000 people have died.

But the nation's actual infection rates are likely several times higher, following recent reports from the Centres for Disease Control and Prevention and warnings from health officials that infections could be 10 times higher than initially reported, suggesting that people who didn't show any signs of symptoms of the disease have transmitted it to others.

Despite Donald Trump's insistence that the surge in new cases is due to the US testing more people, the rate of new infections has outpaced the tests performed. Expanded testing has increased to as much as 780,000 per day within the last two months. Infections should be decreasing within that same time frame – instead they've increased by more than 200 per cent. The US now averages roughly 66,000 new daily cases.

Once the epicentre of the virus, New York's case rate declined, while cases in states that previously had relatively lower positive case rates at the early stages of the pandemic have exploded. California has confirmed more than 400,000 infections, surpassing the total discovered in New York.

New cases – as well as hospitalisations, which have strained bed capacities in many areas – began to climb within an incubation period after stay-at-home orders expired and crowds began to fill once-empty restaurants and bars, Memorial Day and graduation parties, beaches and other events that helped spread the virus.

Nearly 60,000 people were hospitalised for Covid-19 across the US as of Wednesday, nearing the pandemic's April peak.

The CDC also recently confirmed that travel bans that blocked travel to and from Europe arrived far too late, as a dominant European strain of the virus may have circulated in New York City for weeks before the Trump administration – with its focus on China – put restrictions in place.

Those reports underscore a failure to combat the spread of the virus while other countries that once fought dangerous outbreaks have been brought under relative control. Americans have demanded federal and state relief that could alleviate financial and healthcare burdens through the pandemic, limiting closures and keeping sick people at home.

Instead the US has pushed to reboot the lagging economy, aiming for schools to reopen within several weeks without a clear plan how to combat outbreaks among students and faculty that could trigger more infection spikes and closures.

Cases in the US began to spike in mid-June, as states began lifting "lockdown" restrictions and brief quarantine efforts that closed businesses and limited residents' mobility in an effort to keep the virus at bay.

Many states once reluctant to advance stringent stay-at-home orders or mandates that residents wear face coverings have been forced to roll back their openings. More than 30 states have ordered residents to wear masks in public.

The president, who announced his refusal to wear a mask the day the federal guidelines were announced in April, continued to downplay their use, even mocking his political rival Joe Biden for wearing one and suggesting that they're a "politically correct" gesture, amplifying the cultural battle waged by his supporters.

But the day he announced that the administration would resume its near-daily coronavirus press briefings, which were suspended in April, the president shared a black-and-white photo of himself wearing a mask and claimed that "many people say that it is Patriotic to wear a face mask when you can't socially distance. There is nobody more Patriotic than me, your favorite President!"

During the briefing, he said: "We are asking everybody, when you are not able to socially distance, wear a mask.

"Whether you like the mask or not, they have an impact," he added.

He also admitted that "probably, unfortunately" the public health crisis will "get worse before it gets better."

"Something I don't like saying about things," he said, "but that's the way it is.