Over the last week US President Donald Trump has embarked on what many have described as a purge of senior officials in the Department of Homeland Security.

Last Sunday it was announced that the Homeland Security Secretary Kirstjen Nielsen had resigned. According to media reports, President Trump asked for her resignation.

The following day, another senior official at the Department was gone. This time it was Randolph 'Tex' Alles, the Director of the Secret Service. Next to go was Claire Grady, the Homeland Security Undersecretary.

Why is there so much focus on the Department of Homeland Security? Well, because it's the department that looks after border security and immigration.

Earlier this month, it was announced that the Administration would not be proceeding with the appointment of Ronald Vitiello to the role of Director of Immigration and Customs Enforcement because President Trump wanted someone "tougher".

"Ron’s a good man," the president told reporters. "But we’re going in a tougher direction. We want to go in a tougher direction."

Donald Trump's promises of a crackdown on immigration and his 'build a wall' slogan helped him get elected in 2016. With 2020 fast approaching, the US President has his eye on the prize of reelection but in recent months the number of migrants attempting to enter the US has surged.

In March, authorities apprehended or turned back more than 103,000 migrants along the US-Mexico border. Among them were around 53,000 families and almost 9,000 unaccompanied children.

With an average of 3,000 apprehensions per day last month, US Customs and Border Protection officials say they are reaching breaking point.

The previous month was the busiest February for 12 years for US immigration officers with more than 76,000 migrants apprehended. The figures are expected to be even higher this month.

In recent weeks, President Trump has threatened to close the border with Mexico.

According to some media reports, he has even considered reintroducing the controversial policy of separating migrant families at the border.

However, when he was asked about this by reporters this week he said he was not planning to restart family separations and described the practice as an Obama-era policy that he had stopped.

Donald Trump knows that he needs to retain those supporters who chanted 'Build the Wall' at his campaign rallies in 2016.

So far however, keeping that particular promise has been blocked by Congress and the courts.

The reshuffle at the Department of Homeland Security could just be the start of an even tougher approach to border security and it's not clear what will be coming next.

One thing is certain, immigration will be a central issue once again for the Trump Campaign as Election 2020 approaches.