The proposed 3,200-kilometre wall segregating the USA from Mexico was one of the policies defining Donald Trump's presidential campaign. A massive infrastructure undertaking, one of its most controversial aspects is the fact that Trump has stated Mexico will foot the bill - which some experts are estimating at over $25 billion. Understandably, the Mexican government has not shown much enthusiasm for a project no one in their country has asked for. One method suggested by the Trump camp for ensuring compliance has been to prevent Mexican workers in America using wire transfers. But this would be problematic for various reasons.

Pro-Trump Kansas Secretary of State Kris Kobach has commented that blocking this flow of remittances would back Mexico into a corner. They would then have a choice: lose the $23 billion it receives through these channels per annum, or make a single payment to the US to build the wall. Notwithstanding the ethical position of what would amount to state-sponsored blackmail, the problem with these wire transfers is that they are made by Mexicans who are working legally as well as illegally, which would introduce a raft of complications about impounding them.

The US Treasury might then introduce regulations to punish those banks processing Mexican remittances. This would be detrimental to American financial institutions who earn considerable income from overseeing the constant flow of wire transfers. The workers themselves can easily find ways around the wire transfer system to smuggle cash southwards using Bitcoin-like networks.

As with many of the pronouncements made by Trump during his campaign for the Whitehouse, boasting about building a wall captured the imagination of his potential voters. But there are many obstacles standing in the way of it ever becoming a reality.