President Donald Trump has signed an executive order to start construction on the wall along the southern border between the United States and Mexico that was a cornerstone of his election campaign. He recently tweeted: “Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!” But just how practical is his plan?

Why build a wall in the first place?

Trump’s thinking is that a giant wall dividing Mexico and the United States will restrict illegal immigrants’ entry into the country, as he feels the border patrol as it currently stands is weak and letting too many, as he puts it, “rapists” onto American soil.

Like any patriot, Trump sees America as the land of opportunity (but only if you were born there). The wall was one of the first things he promised when he began his campaign in the summer of 2015.

Trump also promised, “I will have Mexico pay for that wall. Mark my words,” which was certainly interesting. Mexico responded very quickly, calling Trump’s comments “prejudicial and absurd.” But despite this, the proposal struck a cord with right-wing voters and he got the Republican nomination and eventually the Presidency, which he’s already using to put the wall into action in his first week.

Trump says his plan to “make Mexico pay” for the construction is “realistic if you know something about the art of negotiating,” but the Mexican Government have said there’s no way they’re paying for it.

Mexico’s President Nieto said, “At the start of the conversation with Donald Trump, I made it clear that Mexico will not pay for the wall.”

The nitty gritty statistics

According to Trump, the wall will be 1,000 miles long and cover the entire US/Mexico border (as natural obstacles take care of the remaining 900 miles). For comparison, the Berlin Wall was just 96 miles long before Ronald Reagan tore it down, while the Great Wall of China is a whopping 13,000 miles long.

When taken to task on the practicalities of his wall, Trump said that, compared to the Great Wall, “we’re talking about peanuts.”

Trump estimates the cost of the construction at $8 billion. For comparison, the current border fence cost $2.4 billion to build. However, Marc Rosenblum, deputy director of the US Immigration Policy Program, estimates the cost of the wall at more like $15-25 billion with annual maintenance costs of $700 million.

That’ll be quite a tax hike.

Despite promising that Mexico will pay “one hundred percent” for the wall during his campaign, Trump is now saying that a spending bill will be used to pay the initial construction fees while he negotiates with the Mexican government for reimbursement. He tweeted that all American spending on the wall “will be paid back by Mexico later!”

Trump does not need Congress to approve construction of the wall

While the likes of the Iraq Resolution usually go to a vote in Congress, Trump is relying on a 2006 law that allows hundreds of miles fencing along the frontier to be built. George W. Bush was President who signed it and it’s called the Secure Fence Act. In any case, Trump’s administration needs approval from Mexico for any structures built along the border due to a border treaty from 1970.

The treaty forbids such structures from disrupting rivers, and there are a bounty of rivers all over the Mexican border all across Texas and much of Arizona, so that throws a major spanner in the works for Trump.

So, any number of things could stand in the way for Trump to fully realise his vision, but for now, it seems very much as though a wall of some shape or form will exist between the US and Mexico in some capacity very soon.