US President Donald Trump has signed his landmark policy bill into law, a day after it was narrowly passed by Congress.

The signing event at the White House on Friday afternoon enacts key parts of the Trump agenda including tax cuts, spending boosts for defence and the immigration crackdown.

There was a celebratory atmosphere at the White House as Trump signed the bill ahead of Independence Day fireworks and a military picnic attended by the pilots who recently flew into Iran to strike three nuclear sites.

Trump told supporters it will unleash economic growth, but he must now convince sceptical Americans as polling suggests many disapprove of parts of the bill.

Several members of his own Republican party were opposed because of the impact on rising US debt and Democrats warned the bill would reward the wealthy and punish the poor.

The 870-page package includes:

extending 2017 tax cuts of Trump's first term
steep cuts to Medicaid spending, the state-provided healthcare scheme for those on low incomes and the disabled
new tax breaks on tipped income, overtime and Social Security
a budget increase of $150bn for defence
a reduction in Biden-era clean energy tax credits
$100bn to Immigration and Customs Enforcement (ICE)

Moments before the bill signing, there was a fly-by of a pair B-2 bombers - the same kind of aircraft that participated in the Iran operation - flanked by highly advanced F-35 and F-22 fighter aircraft.

In a speech from the White House balcony facing the South Lawn, Trump thanked Republican lawmakers who helped usher the bill to his desk. He touted the tax cuts in the bill, brushing aside criticism of the impact to social programmes such as food assistance and Medicaid.

"The largest spending cut, and yet, you won't even notice it," he said of the bill. "The people are happy."

Additionally, Trump praised additional resources being given to border and immigration enforcement and an end to taxes on tips, overtime and social security for senior citizens, which he says the bill will fulfil.

The celebratory mood follows days of tense negotiations with Republican rebels in Congress and days of cajoling on Capitol Hill, sometimes by the president himself.

House Minority Leader Hakeem Jeffries delayed the final vote in the lower chamber of Congress on Thursday by speaking for nearly nine hours.

He called the bill an "extraordinary assault on the healthcare of the American people" and quoted testimony from individuals anxious about its impact.

But his marathon speech only postponed the inevitable. As soon as he sat down, the House moved to a vote.

Only two Republicans went against, joining all 212 Democrats united in opposition. The bill passed by 218 votes to 214.

Earlier this week, the Senate passed the bill but US Vice-President JD Vance was required to cast a tiebreaking vote after three Republicans held out.

Hours after the House passed the bill, the president was in a triumphant mood as he took to the stage in Iowa to kick off a years long celebration of 250 years since American independence.

"There could be no better birthday present for America than the phenomenal victory we achieved just hours ago," he told supporters in Des Moines.

The White House believes the various tax cuts will help stimulate economic growth, but many experts fear that will not be sufficient to prevent the budget deficit - the difference between spending and tax revenue in any year - from ballooning, adding to the national debt.

Analysis by the Congressional Budget Office (CBO) suggests the tax cuts could produce a surplus in the first year but will then cause the deficit to rise sharply.

According to the Tax Policy Center, the tax changes in the bill would benefit wealthier Americans more than those on lower incomes, About 60% of the benefits would go to those making above $217,000 (?158,000), its analysis found.

The BBC spoke to Americans who may see a cut in the subsidies that help them pay for groceries.

Jordan, a father of two, is one of 42 million Americans who benefits from the SNAP (Supplemental Nutrition Assistance Program) scheme targeted by the bill.

He and his wife get about $700 a month to feed their family of four and the 26-year-old said if this bill reduces what he can claim he would get a second job. "I'm going to make sure that I can do whatever I can to feed my family," he says.

Along with cuts to SNAP, the changes to Medicaid - a programme that covers healthcare for low-income, elderly and disabled Americans - would result in nearly 12 million losing coverage in the next decade, the CBO estimates.

Republicans defend their changes to Medicaid, saying that by toughening up work requirements they are tackling abuse and fraud.

Polling taken before the bill passed in Congress suggests public support is low and dwarfed by numbers opposed. A recent Quinnipiac University survey pointed to only 29% endorsing the legislation, which rose to two-thirds among Republicans.

But knowledge of the bill may be low too. Reuters reported there was little awareness of the legislation among Trump supporters they spoke to at the Iowa rally on Thursday night. (BBC)

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