The harping "fake" news media and even congressional Democrats are somewhat sidelined, because in trying to keep his promise to "repeal and replace" Obamacare, Trump must navigate factional trench warfare in his own Republican Party.

The challenge is twofold. The self-proclaimed dealmaker is attempting a sleight of hand, by which millions of his own voters stand to be screwed. More than 80 per cent of them told election day exit pollsters that Obamacare had "gone too far", but experts warn that under Trump's proposed deal they will be slugged for thousands of dollars more a year.

And at the same time, Trump must convince dozens of small government purists in Congress that what is being foisted on them, dubbed Obamacare-lite by some, is not a halfway house that fails to deliver on their absolute commitment to be rid of Barack Obama's legacy-defining health insurance scheme.

Until now being President has been easy-peasy for Trump - keeping his base happy by snarling at the news media, offering a new "he tapped my phones" conspiracy to replace the Obama birther nonsense, firing off another executive order on migration when the first backfired, and shirt-fronting the world on trade and security.

But this conjuring act on healthcare is a very different deal.

On Tuesday, a Trump tweet enthusiastically embraced the replacement package engineered by House Speaker Paul Ryan - "Our wonderful new Healthcare Bill is now out for review and negotiation. Obamacare is a complete and total disaster - is imploding fast".

If "review and negotiation" hinted at a willingness to compromise, Trump seemed to think he was on a winner, saying later: "We're going to do something that's great. I am proud to support the replacement plan released by the House of Representatives."

The more he spoke, the more it seemed that Ryan's plan, formally titled the American Health Care Act, might soon be known as Trumpcare - "It follows the guidelines I laid out in my congressional address - a plan that will lower costs, expand choices, increase competition, and ensure healthcare access for all Americans," Trump said.

Ultimately, voters will judge the plan on its hip-pocket effect and the quality of healthcare.

But it faces a wall of opposition from major doctor and hospital organisations and from one of the country's most powerful lobby groups, the American Association of Retired Persons (AARP); and despite Trump's assurances actuarial predictions are alarming.

The rich will do nicely, thank you very much. Those earning in excess of $US200,000 ($266,000) will benefit most from the elimination of Obamacare taxes. The top 1 per cent of income earners would save up to $US33,000 a year, according to the Tax Policy Centre.

But 90 per cent of Trump voters earn less than $US200,000 a year and half of them are whites who did not go to college. They were key beneficiaries of Obamacare. The Urban Institute calculates that, between 2010 and 2015, the number of non-college educated whites without health insurance fell by 6.2 million, or 39 per cent; and they were the single biggest demographic to get cover under Obamacare in 20 of the 30 states won by Trump.

Under a complex mix of tax credits and shifting premiums as patients grow older, they'll have to pay more to keep their cover under the new deal - by an average of almost $US2500 a year by the time it is fully implemented in 2020.

Whites older than 45, who constituted 56 per cent of Trump's vote, would be hit for almost $US7000 more.

And of the estimated 16 million Americans who gained coverage under Obamacare, financial analysts S&P Global estimate that up to a quarter will end up without cover.

In the guise of a debate on health, a significant redistribution of wealth is being engineered - from the less affluent, including the older, blue-collar whites who steered Trump into the White House, to the well-off.

And so far, there has been little airplay for lofty debate on the notion that the rich might look after the poorest in society. "Even though it is a technical discussion, it's a really big value discussion," Robert Blendon, a professor of health policy and political analysis at Harvard University, told The Washington Post.

Remarkably, the Trump bill has already cleared two House of Representatives committees, which debated through Wednesday night and into the dawn hours of Thursday, without any sense of how much it will cost the government or how many Americans might end up uninsured.

The non-partisan Congressional Budget Office is crunching the numbers - and its findings are vital. If the bill does not save at least $US1billion over 10 years it will cease to qualify as a budget bill, for which the GOP would be able to muster the necessary 51 votes in the Senate; and instead its passage would require 60 votes - which would allow the Democrats to block it.

Despite the early victories in the house committees, Republican Senate Leader Mitch McConnell insisted his chamber needed the costs analysis. "I think we need to know that," he said on Thursday.

Four Republican senators have declared themselves as rebels, opposing the package on the grounds that it offers insufficient protection for those who have cover under Obamacare.

Dead on arrival

And on Thursday, there was an intake of breath in Washington when Trump loyalist Arkansas senator Tom Cotton tweeted that the House needed to "start over" on crafting a replacement for Obamacare. Senator Rand Paul said the bill would be "dead on arrival" in the Senate.

But in the House, Republican opposition to the package is driven by complaints that it was hatched in secret and that it allows too much of Obamacare to survive; they object to taxpayer-funded subsidies to buy insurance, that it allows insurers to charge a penalty for those who allow their insurance to lapse but pick it up later, and that undocumented immigrants could benefit.

A clear picture is yet to emerge on support for the new deal among Republican house members - dozens of whom are aligned with the uber-conservative Tea Party and Freedom caucuses, in a chamber in which 21 Republican defections would block the legislation.

Former house speaker and Trump champion Newt Gingrich seems to doubt its chances, telling a Wednesday lunch: "They're discovering that there are slightly more 'absolutely no [votes]' than you can afford to have. [But] something will get signed into law. I don't have a clue what it will look like. I don't think they do either."

Trump, meanwhile, is proceeding with uncharacteristic caution.

In private meetings the President reportedly has warned members of Congress of a "bloodbath" in the 2018 midterm elections and in 2020 if the bill fails, and he is threatening to hold rallies in the districts of GOP members who refuse to sign on.

But he has stopped short of tweeting nastygrams at Republicans who oppose the bill. He and his staff push back when anyone dares to refer to the bill as "Trumpcare".

There is support for the plan, from its likely beneficiaries - lobbies for those whose corporate and personal income taxes would be reduced, including the US Chamber of Commerce and Americans for Tax Reform.

But on Wednesday, all the big hospital representative groups condemned the bill.

"As organisations that take care of every individual who walks through our doors, both due to our mission and our obligations under federal law, we are committed to ensuring health care coverage is available and affordable for all," they said in a combined statement. "As a result, we cannot support the American Health Care Act as currently written."

The American Medical Association, with about 235,000 members, said it was opposed "because of the expected decline in health insurance coverage and the potential harm it would cause to vulnerable patient populations". By contrast, it said that Obamacare "provides the greatest chance that those of the least means are able to purchase coverage".

Voter backlash

Republicans who support the bill are targeted as traitors - by their own party colleagues. Idaho congressman and influential Freedom Caucus member Raul Labrador warned: "They can go back to their districts and explain to the American people why they lied."

Anna Beavon Gravely, a North Carolina activist demanding the full repeal of Obamacare, told reporters: "I feel lied to."

Giving Trump a dose of his own medicine, she hectored the President: "We trusted you because you said you were going to do something about this. And this is not it. Not even close ... "

Even with control of the White House and both chambers of Congress the Republicans have yet to overcome a failure that has dogged them through the near decade in which Obamacare was on the drawing boards and in service - they've never been able to come up with an alternative on which they can agree as a party.

"They still haven't come up with a workable replacement," The New York Times said in an editorial. "Instead, the GOP's various factions are now haggling over just how many millions of Americans they are willing to harm."

One American getting a lot of air time is Martha Brawley of Monroe, North Carolina, who told reporters she had voted for Trump in the belief he would make health insurance cheaper.

The 55-year-old, who had a liver biopsy on Monday after her doctor diagnosed an autoimmune liver disease, explained that she shells out about $US260 a month as part-payment for an insurance plan on which she also receives an Obamacare subsidy of $US724 a month. But under the Republican plan her tax credit would be just $US3500 a year, which would be $US5188 less than her Obamacare subsidy.

"I'm scared, I'll tell you that right now, to think about not having insurance at my age," she said. "If I didn't have insurance, these doctors wouldn't see me."