Their support for it stems from pain and loss.
Yes, among Trump’s base in America’s heartland there is fear and resentment of illegal immigration, driven by a decline in economic and cultural identity.
And for many in this part of the US, wanting complete control of who comes in and goes out of the country is a matter of common sense, national security and patriotism.
But there’s another reason why the wall matters so much in places hundreds of miles from the border, something that I think supersedes all of the arguments above.
In Ohio, Pennsylvania, Kentucky, Indiana and similar states, entire communities have been changed forever by a miserable rolling crisis of addiction and despair.
In these places, people fervently believe the promise of the man they voted for that a wall will make difference.
It represents hope, a better future, or at the very least, a step towards relief from almost biblical suffering.
I visited West Virginia recently.
Even furloughed workers, missing three pay checks because of the government shutdown over the wall, said they would be happy to sacrifice more if it meant stopping the flow of heroin and fentanyl into their towns.
One business owner told me they had given up drugs testing employees because everyone kept failing.
If being clean remained a requirement to work, there would simply be no-one left to employ.
At a bowling alley, a US Air Force veteran started crying when I asked him about why he supported the wall.
More than anything, he said, he wanted stop the drugs.
He explained that he had lost his son to suicide last year, a tragedy in part fuelled by substance misuse.
He pulled up his left sleeve to reveal his son’s face tattooed on his shoulder, tears falling down his cheeks.
The rest of his bowling team looked on with a kind of resigned sadness.
In Huntington, West Virginia, sometimes called ‘ground zero’ in America’s opioid battle, it has been estimated that as many as one in 10 of the population is addicted.
Last year the local authorities were so overwhelmed by the fallout they called in the National Guard.
In these places there isn’t a family without a story.
It often begins with the furtive overuse of prescription pain killers.
A wisdom tooth, a sprained ankle, a sports injury at football practice, all of these things can set people on a path to destruction.
Addicts function in homes, classrooms, offices, factories, restaurants, clinging to a life that will eventually spiral out of their control.
Public libraries and even high schools have begun stocking Naxolone, the lifesaving overdose reversal treatment.
But addiction gets its hooks in, and many are unable to avoid the very worst that it can inflict – poverty, desperation, needles and death.
If this was your town, your family, your friends, or you, wouldn’t you jump at anything that might stop it?
I’ve written here before about why it is unlikely a wall will do anything at all to stem the flow of drugs in to middle America, or anywhere else for that matter.
But the facts don’t particularly matter when it comes to understanding what’s going on here.
Communities ripped apart by the opioid crisis have made a firm connection between the idea of a barrier on the southern border and an end to their suffering.
Think about that, hard, before you dismiss what they want, and remember that as long as Donald Trump is pushing for the wall, his support in the heartland is almost guaranteed.