Washington DC - President Donald Trump's hardline agenda on everything from immigration to tax reform faced a key reality test in Congress on Tuesday, where Republicans have only an ultra-thin majority and are struggling to agree on a budget.

Members of the House of Representatives are to vote on a resolution that would set the blueprint for the 2025 federal government budget, with $4.5 trillion in tax cuts and more than $1.5 trillion in spending reductions on the docket.

Republican Speaker Mike Johnson, a key Trump ally, has been working to corral his party's lawmakers to back the bill, which Democrats say will result in deep cuts to the Medicaid program that many lower-income families rely on.

Johnson has been pressured from all sides of his own party, too, and on Tuesday hinted that the vote may get pushed back to allow more time to win them over.

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The speaker said Republicans were "very, very close" to a deal, but added: "There may be a vote tonight, there may not be. Stay tuned."

Standing alongside him, House Majority Leader Steve Scalise said talks with lawmakers would continue until the last minute.

"We still have more conversations to have today, just like we do on any day of any big vote," he said.

On the floor of the house, lawmakers opened the debate on the resolution, with the text's sponsor, Jodey Arrington, asserting passage was necessary in order to achieve Trump's agenda.

A number of Republican lawmakers, however, suggest the proposed cuts do not go deep enough, while others are focused on stopping the ever-growing US national debt, and some worry about possible impacts on Medicaid.

Republicans across the country faced opposition to the resolution in its current form at town halls in their constituencies last week, US media reported, with most protests focusing on cuts to social welfare programs.

Trump's party has only a 218-215 cushion over the Democrats in the House, which means it can afford only one defection, assuming all the opposition members vote against this resolution.

On Monday, Johnson conceded that he would likely need to find help from across the aisle.

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Looming over Tuesday's debate is the March 14 deadline for Congress to agree on a budget proposal outline or face a US government shutdown.

For Democrats, this is a test of their willingness to play hardball. So far, they are indicating they will refuse to bail out their opponents.

"Let me be clear, House Democrats will not provide a single vote to this reckless Republican budget. Not one," said House Minority Leader Hakeem Jeffries.

"We will push back against the reckless Republican budget until it is very deep in the ground, never to rise again."

One of the Democratic demands is an assurance that funding approved by Congress is actually spent – rather than being put on the chopping block by Trump's billionaire adviser Elon Musk, whose so-called Department of Government Efficiency is seeking to slash through the entire US budget.

Republicans, however, have shown no sign of willingness to limit Trump's power, with some even seeking to codify Musk's cuts.

Ultimately, the debate on the resolution boils down to where the more than $1.5 trillion in spending cuts that will fund Trump's tax cuts and his signature programs will come from.

With the resolution in its current form, Republicans appear set to have to make huge cuts to Medicaid and other social safety net programs, including food stamps, if they want to fund Trump's tax cuts.

Such a move would put Republican lawmakers in politically vulnerable districts in a weaker position for the midterm elections, due in two years.

Johnson, however, has suggested a different approach: factoring Musk's spending cuts and revenue earned from Trump's rash of trade tariffs into the budget to address the deficit.

"We have new revenue inputs that really ought to be factored into this," he said at a forum on Monday.

Last week, the Senate – where Republicans hold a slim majority – passed a competing budget blueprint that does not include Trump's tax cuts, with leaders saying they would vote on those separately later in the year.

Trump, however, has pushed for "one big beautiful bill" to come from the House, as outlined in the resolution under consideration.

On Tuesday, Senate majority leader John Thune addressed the possibility that the current impasse could lead to another government shutdown.

"We're keeping all options on the table," he said. "But we are running out of time."