President Obama will try this week to achieve something that has thwarted every Democratic president since Harry Truman: health insurance for all Americans.

The campaign to achieve universal health coverage has become the centrepiece of Mr Obama’s domestic agenda, and will involve a titanic legislative battle against well-funded health insurers, pharmaceutical companies and Republicans in Congress.

“It’s time to deliver,” declared Mr Obama in his weekly radio address, demanding that Congress should come up with a Bill by August. Universal healthcare, he said, “is a necessity we cannot postpone any longer”.

The plan is so costly, and the timetable so ambitious, that despite his popularity and big Democratic majorities on Capitol Hill, the President is far from assured of success.

Mr Obama is extremely mindful of the healthcare fiasco that ensnared Bill Clinton early in his presidency, when a gargantuan Bill masterminded by Hillary Clinton, then the First Lady, suffered a humiliating defeat in Congress.

This time, 15 years on, Mr Obama is leaving Congress to draft the legislation, but in recent days he has decided to take greater control of the debate, hoping to use his popularity to increase momentum behind the measure.

He is to deliver speeches, hold town-hall meetings — beginning on Thursday in Wisconsin — and at the weekend mobilised a grassroots network of two million supporters to rally support across all 50 states.

Mr Obama wants to extend healthcare to the 46 million people in America who do not have coverage, and to ensure that all citizens have access to medical treatment. He also wants to improve the quality and lower the costs of medical care.

A key figure in the drafting process is Senator Edward Kennedy, a lifelong advocate of universal health coverage, who has brain cancer.

Last week Mr Obama announced the broad outlines of his approach. The most controversial element is a government-run healthcare plan that would compete with private plans, something that is fiercely opposed by Republicans and insurance companies.

Mr Obama also now appears willing to tax health benefits as income to help to pay for the programme — a move that he opposed as a candidate and that business is mobilising against.

The central question that the White House has failed adequately to answer is how Mr Obama intends to pay for a plan that is projected to cost $1.2 trillion (£750 billion) over ten years, at a time of rocketing deficits, historically high stimulus spending and financial sector bailouts.

Only half of that sum is covered by Mr Obama’s plan to raise taxes on the wealthiest Americans.

Republicans appear almost unified in opposition, and many fiscally conservative “Blue Dog” Democrats in the House are opposed to an expensive government-run plan.

Mr Obama is also asking Congress to draft and push through what amounts to the biggest social spending programme in US history in a matter of months, a schedule that is angering Republicans and even causing alarm among some in his own party.

Mr Obama has declared that this summer is “make or break” time for getting universal health coverage, and he is probably right. He is riding high in the polls and has big majorities in the House and Senate. If a Bill has not cleared Congress by the autumn, it probably never will.

Already, conservative groups have launched advertisements warning of “socialised” medical care and long waiting lists. In a sign of how rancorous the debate has become, Senator Chuck Grassley, the leading Republican on the Finance Committee, sent a Twitter message while Mr Obama was in Paris this weekend.

“Pres Obama you got nerve while u sightseeing in Paris to tell us ‘time to deliver’ on health care,” Mr Grassley wrote, adding that many senators were working at the weekend.

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