Donald Trump says he will almost definitely declare a national emergency if Congress fails to bend on his demand for billions to fund a border wall.
US President Donald Trump has threatened to use emergency powers to bypass Congress to pay for a wall on the US-Mexico border.
Trump flew to the Texas border with Mexico to try to bolster his case for the border wall as a partial US government shutdown tied to the issue stretched into its 20th day with no sign of new talks to resolve the impasse.
"We can declare a national emergency. We shouldn't have to," Trump told reporters. "This is just common sense."
Such a step would likely prompt an immediate legal challenge over constitutional powers from congressional Democrats.
The Republican president is adamant that a government funding bill to end the shutdown include $US5.7 billion for a border barrier - his signature campaign promise. Congressional Democrats oppose that.
A day after he stormed out of a meeting with Democratic leaders, Trump attacked them for refusing his demand, calling them harder to deal with than China, a rival power.
"I find China, frankly, in many ways to be far more honourable than Crying Chuck and Nancy. I really do," Trump said, referring to House of Representatives Speaker Nancy Pelosi and Senate Democratic leader Chuck Schumer.
The House passed two bills to fund the departments of transportation, housing and agriculture - each drawing a few more Republican votes than a similar effort on Wednesday to reopen the Treasury Department and other agencies.
The White House has said Trump would veto the bills if they made it to his desk.
Trump cancelled plans to attend the World Economic Forum in Davos, Switzerland, scheduled to start on January 22, signalling he was prepared for the shutdown to drag on.
Trump said his lawyers had told him he had the power to invoke national emergency powers to get his wall funded.
"I have the absolute right to declare a national emergency," Trump told reporters at the White House.
"I'm not prepared to do that yet, but if I have to, I will."
The declaration would circumvent Congress' power over the national purse strings. A subsequent court fight could be protracted.
The Washington Post, citing sources, reported that the White House was laying the groundwork for declaring an emergency that would let Trump build sections of a wall, possibly using funds from the Army Corps of Engineers.
NBC News, in a similar report, said Trump had been briefed on the plan involving the Army Corps while flying to the border on Thursday. A White House official denied Trump had been briefed on the plan, and the Pentagon declined to comment on the news reports.
Pressure on both sides could intensify on Friday when about 800,000 federal employees miss their first pay cheques. About half of them are deemed "essential" to national security, like prison guards and airport security screeners - and have to continue working. Others are home on furlough.
At the FBI, where most agents continue to work, concerns are building that operational funds the bureau needs to conduct investigations, including sensitive undercover operations, are beginning to dry up, said Tom O'Connor, president of the FBI Agents Association.
The shutdown, which began on December 22, will be the longest in US history if it is still going on by Saturday.