Posturing to be working hard on a solution. One that drives well with far right voters who hate foreigners.
The alternative of working on the cause instead of the symptom would put pressure on wealthy business owners and look like overreach to those voters.
There’s a sort of twisted reason, though. Fascists need a manufactured enemy to whom they can attribute blame for society’s ills – in this case, the myth of a “border crisis.” It’s sadly effective too, and somewhere around 70% of right-wingers in the US believe it, many of whom are so ignorant they don’t realize they’re complicit in bolstering fascism.
It’s simply part of an effort to impose moral beliefs on a world that to them, appears to work without them. Bringing order to chaos. Kind of like the Christian beliefs underpinning such cruelty.