President Donald Trump threatened Tuesday night that he might shut down the federal government unless Congress provides funding for his promised border wall between the U.S. and Mexico.

'Now the obstructionist Democrats would like us not to do it,' the president said during a rally speech in Phoenix, Arizona.

'But believe me: If we have to close down our government, we're building that wall.'

Trump also accused congressional Democrats of putting American security at risk for not supporting the proposal, which was one of his marquee campaign pledges.

'We are building a wall on the southern border, which is absolutely necessary,' he said.

'Let me be very clear to Democrats in Congress who oppose a border wall and stand in the way of border security,' Trump continued: 'You are putting all of Americans' safety at risk.'

President Donald Trump (seen above at a campaign rally in Phoenix on Tuesday) threatened Tuesday night that he might shut down the federal government unless Congress provides funding for his promised border wall between the U.S. and Mexico

'Now the obstructionist Democrats would like us not to do it,' the president said during a rally speech in Phoenix, Arizona. 'But believe me: If we have to close down our government, we're building that wall'

Tuesday night's crowd, thousands strong, erupted at one point in chants of 'Build that wall!' – a repeat of audiences at countless campaign events.

Trump promised repeatedly during his run for the White House that Mexico would pay for the wall, but America's neighbor to the south has rejected the idea.

The administration has since suggested that although taxpayers will fund the wall's construction, Mexicans will foot the bill in the long term through fees charged to border-crossers and taxes levied on monetary remittances sent from U.S. residents to Mexicans.

The House of Representatives has passed a spending bill with partial funding for the border wall amounting to $1.6 billion, but it faces an uncertain future in the Senate.

The House of Representatives has passed a spending bill with partial funding for the border wall amounting to $1.6 billion, but it faces an uncertain future in the Senate. A portion of the metal border fence separating Mexico and Arizona is seen in the above stock image

The Department of Homeland Security has already begun to accept design proposals for a border wall, requiring a minimum of 18 feet in height and anti-climbing and tunneling features.

Potential vendors were also instructed to make designs 'aesthetically pleasing' – on the side that faces the United States.

Trump said Tuesday that illegal immigration was a major reason voters set him to the White House, and reminded a national TV audience that he had met repeatedly with 'angel moms,' parents of people killed by criminal aliens.

'I promised these families the deaths of their loved ones will not have been in vain,' he said.