1. The Great Wall is a lot longer. Even without the many branches it’s equivalent to about twice the width of the USA.
2. Those who conceived and ordered its construction – mostly the Ming Dynasty emperors – would, I think it fair to say, have been wiser, more erudite and much broader of mind and vision than the creature known as Trump.
3. It was built to protect the most enduring of the world’s great ancient civilisations from attack by barbarian hordes. The real threat posed by mediaeval Mongols was not quite the same as the current perceived threat from modern Mexican migrants. And, let’s be honest, the USA is not exactly a great ancient civilisation.
There is, however, one similarity which might come to fruition. For all its might and expert engineering, the Great Wall ultimately failed to keep the Mongols out. Time will tell.