The teaser accomplishes a lot in just a short amount of time. Obviously, it whet everyone’s appetite for the movie, but it also did tons of narrative leg-work. First of all, it set up the idea that more Terminators can be easily constructed, hence how the killer robot from the earlier movie returns. But most importantly, it primed audiences for the big plot twist, one that the movie’s opening act crafts carefully; the T-800 is John Conner’s protector now, and the T-1000, the cop who seemed human, is the evil robot. The teaser was a brilliant piece of misdirection, making it seem as though yet another villainous Terminator was being built to finish the job he started in the first movie. What we don’t see is the moment in the story when grizzled future John Connor reprograms him. 

Unfortunately, what should have been one of the greatest twists in movie history was totally screwed over by the full theatrical trailer.