WASHINGTON — Donald Trump pressed for the funding of a Mexico border wall on Sunday as a looming spending showdown in Congress threatens to shut down the US government on the president’s 100th day in office.

Building the wall was Trump’s signature campaign promise, and the White House appeared determined to get Congress to approve a down payment as part of a bigger bill to keep the US government funded.

Trump weighed in on Twitter, insisting Mexico will pay for the wall "but at a later date so we can get started early."

"The Democrats don’t want money from budget going to border wall despite the fact that it will stop drugs and very bad MS 13 gang members," he wrote.

White House budget chief Mick Mulvaney said the administration is prepared to make concessions to Democrats on health care reform in order to get the wall money.

But if the wall isn’t funded, will the president veto the larger spending bill, risking a government shutdown on Saturday - coincidentally Trump’s 100th day in office?

"Don’t know yet," Mulvaney said on Fox News on Sunday. "We are asking for our priorities and importantly we are offering to give Democrats some of their priorities as well."

The specter of a government shutdown has often loomed over US budget negotiations. The threat has most often been averted - but has come to pass several times, most recently for 16 days in 2013 amid a dispute over funding for Barack Obama’s signature health care reforms.

Record low approval

The fight this time comes as the White House is eager to show off Trump’s accomplishments at the 100-day mark.

The president is planning a speech to the nation and an "America First" rally on Saturday to highlight his successes, accompanied by an outpouring of digital content.

Trump surprised his own aides last week by promising a big announcement on tax reform last Wednesday even though lawmakers have yet to conclude negotiations on health reform, a major variable in government spending.

Mulvaney said it would be a statement of principles rather than legislation, "with some indication what the rates are going to be."

"I don’t think anybody expects us to roll bill language on Wednesday," he added.

Although he has slashed government regulations and used his executive powers more frequently than any of his recent predecessors, Trump has had no major legislative achievements to speak of so far.

His attempt to repeal and replace his predecessor’s health care reforms was rejected in the Republican-controlled Congress, and his executive order imposing a travel ban targeting citizens of several mainly Muslim countries as well as refugees has been blocked by the courts.

A new Washington Post/ABC News poll showed his approval ratings to be at a record low for a modern US president at a point in office when most have still enjoyed a honeymoon.

It found that 42 per cent of Americans approved of his performance and 53 per cent disapproved.

Trump nevertheless found a silver lining in the poll numbers.

"New polls out today are very good considering that much of the media is FAKE and almost always negative," he tweeted.

"Would still beat Hillary in popular vote," he said, referring to Democrat Hillary Clinton, whom he vanquished in last November’s presidential election.

"ABC News/Washington Post Poll (wrong big on election) said almost all stand by their vote on me & 53 per cent said strong leader," Trump gloated about the survey’s findings.

Spending compromise?

Democrats, meanwhile, have shown little interest in compromise, particularly on the border wall project.

"I hope the president will back off," said Senator Dick Durbin, the number-two Democrat in the Senate, on CNN’s "State of the Union".

"To think that he would consider shutting down the government of the United States of America over this outlandish proposal of a border wall, which we can’t even pay for at this point, and is opposed by Democrats and Republicans all along the border, that would be the height of irresponsibility," he said.

However, Mulvaney insisted that "shutdown is not desired and it’s not a tool, it’s not something we want to have.

"We want our priorities funded and one of the biggest priorities during the campaign was border security, keeping Americans safe and part of that was a border wall."

US Attorney General Jeff Sessions and Homeland Security Secretary John Kelly made similar pitches on other television talk shows.

"I think it’s certainly worth hard negotiation over," Kelly said on CBS’s "Face the Nation".

"We have tremendous threats, whether it’s drugs, people, potential terrorists, coming up from the south."

Sessions said Trump would decide whether the wall money was worth the risk of a government shutdown.

"But I know one thing, we need that wall," he said on ABC’s "This Week." "It will help us complete the promise that the president has made to the American people. That’s what they want." — AFP