After a contentious and unproductive meeting between US President Donald Trump and Democratic lawmakers on Wednesday, there is still no end in sight for a partial US government shutdown.

As the paychecks of 800,000 federal government workers hang in the balance, Trump has said he will refuse to sign any legislation to fund the government agencies affected until Congress agrees to earmark US$5.6 billion to spend on a physical barrier on the southern border with Mexico.

The president walked out of negotiations with Democratic House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer Wednesday afternoon after Pelosi said she would not support wall funding.

“Just left a meeting with Chuck and Nancy, a total waste of time,” Trump wrote on Twitter.

Schumer responded during a press conference after the meeting that Trump’s decision to abruptly walk out of the meeting was “really, really unfortunate and in my judgment somewhat unbecoming of a presidency.”

Short of negotiating a deal with Democrats, it would theoretically be possible for Trump to divert funds for the wall from the Pentagon by declaring a national emergency. Reports have indicated the president is increasingly likely to attempt this, though lawmakers, including some in his party, warn that such a move would likely be challenged in the courts.

Already in its 19th day, the current shutdown is set to extend longer than the 21-day 1995-96 shutdown, the longest in modern American history. Around 420,000 federal government employees are now working without pay, while another 380,000 are on unpaid leave.