YUMA, Ariz. (AP) – President Donald Trump says his administration plans to build up to 500 miles (805 kilometers) of border wall by the end of next year, and plans are already taking shape in Arizona and elsewhere.

But some are skeptical about whether the goal announced this week is achievable or even necessary.

Construction crews south of Yuma, Arizona, are putting up tall fencing along 5 miles (8 kilometers) of U.S.-Mexico border. The section is replacing shorter barriers meant to keep out cars, but not people.

The Border Patrol says tens of thousands of people have crossed the border illegally through the area and that the existing barriers don’t suffice.

While the number of people apprehended by the Border Patrol is up in Yuma compared with last year, the figure has dropped dramatically there and across the southern border over the past few months