
Border fence between San Diego's border patrol offices in California (left) and Tijuana, Mexico (right). Public domain.
Part of the justification for President Donald Trump’s “great wall” is that it is needed to keep America protected from what lies below – northern Mexico is rife with drug violence and there exists a very real risk of that violence spilling over into American cities and towns.
But the dynamics of the drug trade – and the numbers – point to a different reality.