At the end of The Post (2017), security guard Frank Wills discovers a break-in in progress at the Watergate complex.
Why does the movie end at the beginning of the Watergate scandal?
The movie had this to show that although the Pentagon Papers were a huge scandal at the time, there were even bigger scandals waiting in the wings to be revealed.
Again, by the Washington Post, (in the form of Woodward & Bernstein). See All The President's Men
There's a comment after the Court renders it's verdict that the case is over and they can start to get back to normal without fear of prosecution.
Because you know I don't think I could ever live through something like this again.
...and then the Post is banned from the White House and we move over to the start of the Watergate scandal coming into shape.
The Pentagon Papers laid the strongest foundation for freedom of the press to investigate and reveal governmental wrongdoing.