No trailer, synopsis, nothing?
TFR standards these days
It's a De Niro directed film about the early days of the OSS/CIA.
Damon's character is said to mirror famed counter intelligence officer James Jesus Angleton, but more accurately serves as a proxy for the glamorous and insular Groton/Yale establishment types who once ran the American spy agency.
In real life, after being betrayed by Kim Philby, Angleton became convinced of there being a mole inside the agency and spent a couple decades trying to locate him. He ruined a number of careers in the process and was ultimately forced to resign after an investigation into his conduct (likely a result of other Church committee investigations into CIA conduct).
Establishment types don't really exist at the agency anymore (now filled with Mormons) and it's impossible for most to understand just how much influence they had.
Movie is long and not always focused but worth the watch if you're interested in this era of intellectuals, wonks, and establishment types. Also check out books:
The Very Best Men - Evan Thomas
The Wise Men - Evan Thomas/Walter Issacson
The Best and the Brightest - David Halberstam
There is an old PBS Frontline about Angleton called uh, "The Spy Hunter" though, you're unlikely to find it anywhere online.