Part of the fence that already stretches along the Mexican border near Naco, Arizona. Thomson Reuters A Republican sheriff from a county on the US-Mexico border said President Donald Trump's approach to dealing with immigration isn't feasible, or morally right.

Mark Napier, a sheriff in Pima County, Arizona, told The New York Times' "The Daily" podcast that he doesn't believe Trump's plans to build a wall on the Mexican border is a "feasible solution."

As a large county in southern Arizona, Pima shares 125 miles of border with Mexico and would be one of the sites for Trump's proposed wall. Earlier this year, Napier told the Times that his team doesn't "have excess capacity to engage in proactive federal immigration enforcement."

After Trump's recent attempts to crack down on undocumented immigrants, Napier said he's seen a decline in people crossing the border legally, due to "a climate of uncertainty about how they will be treated" — which has a detrimental effect on the state's economy. He said trade with Mexico is a $9 billion industry in Arizona.

"I would ask my Republican brotherhood that decry [undocumented immigration], 'if you family were impoverished, if your family were endangered, if your family were in need, what would you not do to protect them?'" he said.

Napier also argued that he'd be able to keep his county safer with a fraction of what it costs to build the wall, if Trump and Congress simply decided to allocate any wall funds to law enforcement instead.

"You'd have to argue that it's a feasible proposition to begin with, and I'm not sure that I subscribe to that," he said. "I think it's kind of a medieval solution to a modern problem. I mean, 10,000 years ago we were building walls around things, and here we are in 2017, and this is the best idea we can come up with?"