Around 800,000 US federal workers will not receive their pay cheques today because of the partial government shutdown.

The shutdown, which is in its 21st day, is taking place as a result of a row over funding for Donald Trump’s controversial wall along the US/Mexico border.

Tomorrow, the partial closure of the government will become the longest in US history.

Even some lawmakers in the US President's Republican Party are wavering in their support for the president as the shutdown causes difficulties for their constituents.

Mr Trump has once again threatened to declare a national emergency as he seeks funding for the wall, which he says will keep out dangerous immigrants.

Such a declaration, almost certain to be challenged in court, would in theory allow Mr Trump to sidestep Congress and divert money from military projects toward construction of the wall that has been a core focus of his nationalist campaign.

Speaking to Fox News in an interview yesterday, Mr Trump reiterated he had "the absolute right to declare a national emergency".

However when pressed on a timeline for doing so, he said he would "see what happens" over the coming days.

Read: As Trump visited the border, protesters visited the White House

Analysts say the declaration would likely be challenged as a case of presidential overreach, which means the wall could still face being blocked.

However, it would give Mr Trump political cover with his base by showing he had done what he could to build the wall. At that point, Mr Trump could end the shutdown and declare a win.

Yesterday, the US President toured the border with Mexico to press his case for a wall and warned of murderers and gangsters spreading across the country.

He used the backdrop of the Rio Grande border river at McAllen, Texas, to ramp up what has already turned into a hugely messy political fight with Democratic opponents.

Opposition Democrats are refusing to approve $5.7bn in wall funding, saying that overwhelming numbers of illegal immigrants do not commit serious crimes and that Mr Trump is mainly promoting the project to satisfy his right-wing base.

He said that illegal immigrant crime stretched right up into the north of the country.

However, widely respected studies show that illegal immigrants commit fewer crimes than people born in the United States.