In it, they link the assassination of John F. Kennedy to Magneto. Makes sense, right? He can move metal, so he could be the force behind the magic bullet. This (I hope) is what will set the stage for the plot of the movie. In the comic book storyline, it's Magneto's Brotherhood of Evil Mutants who are responsible for the killing of Senator Robert Kelly, which takes the world down a terrifying path, causing the need to travel back in time.
Unfortunately (actually, not unfortunately), Senator Kelly was killed in the first X-Men movie. So he can't be the main plot point for Days of Future Past. Does that mean instead the movie revolves around the assassination of Kennedy and Wolverine trying to prevent it? I just got chills writing that sentence. FUCK AND YEA.
There's also a whole website about the assassination if you want to waste your day (I did).