The fake news in question is the centerpiece of the episode. We saw O'Keefe putting it together previously. Its footage manipulated to look like the President-elect's son, killed in Afghanistan, was actually running away like a coward and was not a hero. As such, this bears resemblances to what the GOP did to John Kerry with the notorious "swift boat" ads in the 2004 election, and Bowe Bergdahl's true story in Afghanistan, though the Kerry and Bergdahl stories have nothing else in common.
In Homeland, O'Keefe unleashes this caustic fake news at Dar's request, after the President-elect spurns his "advice" to appoint people to her cabinet who attacked her in the election, and tells him she intends to put his "ass in jail". Not one to be bullied, Dar goes nuclear and launches O'Keefe.
In a sweet twist - though sweet is likely not the best word for this - Saul ends up being the only person who can help the President-elect now, courtesy of the video Max sent to Carrie, which shows O'Keefe and Dar talking. This means Saul won't have to leave the country.
If I hadn't titled this review "Fake News," I might have gone for "The Education of the President-Elect," as she's certainly wised up now to what Dar is, and some of what's been going on. She realizes that Dar is pulling Carrie's strings via Franny, and no doubt regrets that she didn't come to Carrie's aid when Carrie practically begged her for help.
Better late than never, and it will be fun to see Carrie, Saul, and the President-elect in an all-out war against the intelligence establishment on Homeland. As to how this is reflected in the Trump administration - I'll leave that for another review.
And see also Homeland on Showtime ... Homeland 1.8: Surprises ... Homeland Concludes First Season: Exceptional