Trump's State of the Union speech could become a casualty of the partial shutdown after House Speaker Nancy Pelosi asked President Donald Trump to postpone his January 29 address.

The longest such shutdown in USA history dragged into its 25th day with neither President Donald Trump nor Democratic congressional leaders showing signs of bending on the topic that triggered it - funding for a wall Trump promised to build along the border with Mexico.

Pelosi had written to the president on Wednesday asking him to delay his State of the Union address, as the ongoing government shutdown would mean federal law enforcement officers would be working the event without pay.

The shutdown began on December 22 after Trump insisted he would not sign legislation funding the idled government agencies unless it included more than $5 billion for the border wall.

House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer have offered $1.3 billion for border security, but Pelosi has ruled out any funding for Trump's wall.

The group released a statement saying they met with Trump in the White House Situation Room regarding the shutdown.

The uncertainty surrounding the speech also underscored the unraveling of ceremonial norms and niceties in Trump's Washington, with the shutdown in its fourth week, the White House and Democrats in a stalemate and the impasse draining the finances of hundreds of thousands of federal employees.

The nation's two most powerful leaders appeared to be engaged in a game of constitutional one-upmanship as negotiations to end the monthlong partial government shutdown failed to produce results.

"Republican support for the wall is at record high, while Democratic support has reached a new low", the Pew said in a report, reports Xinhua news agency.

Trump had previously shot down that suggestion, insisting that he wouldn't accept a deal to reopen the government without an agreement on wall funding, and White House officials were pressing Republican senators to not sign the new letter, The Washington Post reported. The House and Senate had voted to give the workers back pay whenever the federal government reopens.

800,000 federal workers are going without pay during the shutdown.

The U.S. Department of Agriculture said it was recalling about 2,500 furloughed Farm Service Administration employees to assist farmers with existing loans and ensure the agency meets a deadline for providing tax documents.

President Donald Trump has told supporters in a conference call that the shutdown will continue, in his words, "for a long time" if it has to.

"The Democrats are not going to negotiate with the government shut down", he said.

Trump has said he won't sign legislation without money for his promised wall at the border with Mexico.

Economists have estimated that each week the shutdown continues will shave off 0.1 percent of economic growth.

The shutdown, now in its 26th day, affects nine government departments, including the Department of Homeland Security, of which the Secret Service is a component.

Trump, who a week ago seemed intent on declaring a national emergency in order to build the wall, has turned his attention back to Congress as polling shows he is taking much of the blame for the standoff. They're from a bipartisan group called the Problem Solvers Caucus.