Unless I'm mistaken, the US-Mexico border is already closed to all but essential traffic. Are you arguing for closing it to essential traffic too?
My point: If you're concerned about hot spots why not freaking hermetically seal the land and sea borders to a place like Florida, let no one in or out, and let that raging forest fire of a plague burn itself out there. Cases are rising all over the states I listed (probably correlated to vaccination rates and Disney World vacations as well, but I don't care enough to look it up). Or you can blame Mexico. Closing the Mexican border is not THE solution to the problem.