Donald Trump's Unfinished Business

The reason that administration gave for building trump's wall in these sections of arizona is because they're saying it's dangerous for migrants to cross the river there, and so they want to put up a wall. But now they're say that walls do stop people from crossing, yes, but they're only doing it here because they want to make it safer. Although if you really wanted to make crossing a river safer, then why wouldn't you just build a bridge? That's rightyes, this doesn't make sense.