The US can grab Greenland, Mexico, and Canada. Militarily, it’s straightforward. The US is so extremely superior, nobody will be able to stop them. 

The US is self sufficient in oil. It doesn’t even need Venezuelan oil. 

This situation isn’t comparable to Nazi Germany at all. Germany is in Central Europe and has major land powers in France and Russia plus the UK to contend with. The USA sit safe and sound, protected by vast oceans on both sides.