It might not be true people can simply cross our border with NO interference... I mean, obviously we DO still have border checkpoints and some barriers to entry put in place. We do hire border patrol people and we have an immigration enforcement group.
But the point is, we're getting floods of people coming through who are NOT getting vetted, and many people who get caught trying to cross illegally are just sent back across to the other side so they can attempt it again another day.
The "MAGA agenda" of "build a wall" is kind of a simple-minded attempt at a solution. Realistically, we had previous Presidents try to ensure a continuous wall was built along our Southern border and the plan failed. They didn't realize how complicated it was going to be to try to use a lot of that privately owned land to construct a wall along it. (Eminent domain would be required and the courts would be tied up for decades fighting every farmer along the way.) Perhaps America lacked the foresight to reserve a strip of land around all of our borders as government-owned, from the very start? (Our public utilities have easements but our own borders apparently don't.)
Still, our 2 party political system forces everyone to choose between two, often lousy, options, to go with the one more closely resembling one that gets the results they want to see. Right now, that "MAGA agenda" is looking slightly superior to the status-quo to me.