LONDON — President Trump took a swing at Britain’s beloved National Health Service on Monday, tweeting that Britons were marching in the streets because their universal health-care system was financially strapped and dysfunctional, and got a swift rebuke from the British prime minister.

“The Democrats are pushing for Universal HealthCare while thousands of people are marching in the UK because their U system is going broke and not working. Dems want to greatly raise taxes for really bad and non-personal medical care. No thanks!” he wrote.

But the thousands of Britons who took to the streets over the weekend were marching in support of the NHS and calling for greater government funding.

Trump's tweet about Britain’s universal health-care system — once said to be the closest thing that the British have to a national religion — provoked ire from across the political spectrum, including from British Prime Minister Theresa May.

A spokesman for May said that “the prime minister is proud of our NHS, that is free at the point of delivery.” The spokesman said that funding “is at a record high and was prioritized in the budget with an extra 2.8 billion pounds. In the recent Commonwealth Fund international survey, the NHS was rated the best in the world for a second time.”

Jeremy Hunt, Britain’s health secretary, said he is proud to hail from a country where people have coverage “no matter the size of their bank balance.”

Opposition leader Jeremy Corbyn of the Labour Party said that Trump was “wrong,” adding: “People were marching because we love our NHS and hate what the Tories are doing to it. Healthcare is a human right.”

The march was called “NHS in crisis: Fix it now” and was organized by the People’s Assembly and Health Campaigns Together. Demonstrators carried placards that read: “NHS: More staff, more beds, more funds” and “Saving lives costs money, Saving money costs lives.”

Responding to Trump’s comments, the march organizers said they were campaigning against a U.S.-style health-care system that they said is “expensive, inefficient and unjust.”

It’s hard to overstate just how proud Britons are of their “free at the point of use” health-care system, established after World War II. Some have pointed out that Britain spends a lower percentage of its GDP on health care than the United States does and that life expectancy is longer in the United Kingdom.

In the opening ceremony for the 2012 London Olympics, the NHS was celebrated with a dance sequence with nurses and patients. In the lead-up to the Brexit vote in June 2016, the pro-Brexit side famously said that leaving the bloc could mean that an extra 350 million pounds ($467 million) a week could be spent on health care.

“We send the EU £350m a week — let’s fund our NHS instead,” was the slogan plastered on the side of a red campaign bus.

Few things unite the British like an outsider complaining about their universal health care. But within the U.K., there is widespread concern about the financial health of the NHS. Britain’s aging population, the rising cost of new technology and years of austerity have contributed to notable pressures on the system.

Britain has also had, once again, a terrible winter flu season, and hospitals nationwide are struggling to cope with the spikes in demand.

“There is widespread concern that austerity we’ve seen in the last seven years has basically put the NHS on its knees. In an attempt to drive efficiency in the system, to deliver the same for less money, we are now seeing poorer quality of care,” said Harry Quilter-Pinner, a research fellow at the Institute for Public Policy Research, a London-based think tank.

“Waiting times for elective treatments, for cancer, for example, have gone up. Waiting times for GPs have gone up. Hospitals are missing targets for how long you wait at A&E [accident and emergency],” he said.

Still, there is no public appetite for privatized health care. “The [British] system is still one of most efficient ways of funding and running a health service, it just needs more money,” Quilter-Pinner said.

The NHS contretemps are just the latest between May and Trump. In November, the British leader said that Trump was “wrong” to retweet anti-Islam videos from a far-right British group. He shot back saying that she should focus on “destructive radical Islamic terrorism” in the U.K.

There is speculation that Trump’s tweet might have been inspired by a segment on the NHS by Fox News Channel, which the president frequently watches. In fact, he followed up his tweet on the NHS by thanking Fox News for “exposing the truth.”

Nigel Farage, a former leader of the UK Independence Party, was on the Fox News segment, saying that Britain’s health service is “pretty much at a breaking point” because of a “population crisis.”

“We just haven’t got enough hospitals, we haven’t got enough doctors, we haven’t got enough facilities,” he said.

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