Washington DC - The Republican-led Congress adopted a budget Thursday that unlocks trillions of dollars for President Donald Trump's agenda, jump-starting what Democrats say is a plan to dismantle social welfare in favor of tax cuts for the rich.

House Speaker Mike Johnson said the blueprint would deliver on promises Trump made in his election campaign, including "historic" spending reductions, as well as an extension of his expiring 2017 tax relief.

"We want to make government more efficient, effective, and leaner for the American people, and I think that will serve every American of every party, and we're happy to do that," Johnson told reporters in a briefing at the US Capitol.

But opponents say the framework will trigger a major downsizing of essential services, after Trump's tech billionaire advisor Elon Musk led a campaign of slashing federal agencies.

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The budget resolution raises the country's borrowing limit by $5 trillion to cover a renewal of Trump's expiring 2017 tax cuts through 2034, expected to add roughly the same amount to the country's debt.

Democrats say it is the opening salvo in long-held Republican plans – spelled out last year in the conservative Heritage Foundation's "Project 2025" manifesto – to drastically rein in the federal bureaucracy.

The budget blueprint, which passed the House after getting the green light Saturday in the Senate, sets targets for overall spending and mandates $4 billion in cuts.

But Republican leaders in both chambers are eyeing much more ambitious savings of $1.5 trillion, including $880 billion that opponents say would have to come mostly from the Medicaid health care program for low income families.

Democrats have voiced fears that Trump will also break his promise not to touch Social Security – the federal welfare program for seniors and the disabled that makes up more than fifth of federal spending.

They argue that Trump's 2017 tax cuts disproportionately benefited wealthy individuals and corporations, and extending them would compound inequality.

House Minority Leader Hakeem Jeffries blasted Republicans for what he called "the largest Medicaid cut in American history in order to pass massive tax breaks for your billionaire donors like Elon Musk."

"House Republicans broke their promise to address the high cost of living, and they lied about their intention to enact their extreme Project 2025 agenda," he said in a letter to his members.

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"The harm being unleashed by Donald Trump and the [Republicans] is staggering."

The two sides of Congress were required to adopt identical versions of the budget before lawmakers can move on Trump's domestic agenda, led by the tax relief, beefed-up police presence at the border, and boosted energy production.

It advanced from the Senate with votes to spare but barely made it through the rubber-stamp vote in the House, put in jeopardy by a rank-and-file rebellion over spending cuts.

Both chambers of Congress are Republican-led, but right-wing fiscal hawks in the House were furious over what they saw as insufficient cuts in the final version after it was amended by the Senate.

Johnson vowed to pursue his much more ambitious $1.5 trillion spending cuts figure, and this public commitment appeared to have assuaged some on his back benches.

Final passage of the budget will be a relief to Trump, after opposition within his party exposed limits to his iron grip and raised doubts over the Republicans' ability to coalesce around his agenda.