Warning: Contains SPOILERS for The Handmaid's Tale season 4, episode 9, "Progress."
Fred Waterford decides to turn against Gilead in Waterfords' trial in Canada, where it seemed like the pair could finally face some semblance of justice for their crimes. June's powerful testimony before the International Criminal Court laid the groundwork for the pair to be found guilty, but Fred found a way to worm out of it.
The Handmaid's Tale season 4, episode 9, "Progress," sees Serena and Fred paid a visit by some old friends from Gilead, Commander Warren Putnam and his wife, Naomi. However, what at first seems like a friendly visit quickly transpires to have ulterior motives: the Putnams want to take in the Waterfords' child once it's born, clearly believing that Fred and Serena have no chance of returning to Gilead. For the part of Gilead itself, it won't help them any either.
That leads to Fred's shocking decision, as he agrees to tell all in exchange for immunity and his freedom. It's a pivotal moment for The Handmaid's Tale's future, and rightly provokes a furious response from June. Mark Tuello has essentially played her, using what evidence she can and then moving on to something bigger when the opportunity presents itself. From Mark's point-of-view, while the morality of it is extremely questionable, it is also somewhat understandable: few people from Gilead can give the kind of information, secrets, and names that Fred Waterford can. He is not only a man on the inside, but one who knows almost all of its workings (or at least, did until he left for Canada), and where plenty of the bodies are buried.
The testimony and evidence that Fred gives could well be damning for Gilead. Whereas June's evidence was damaging to the Waterfords, it seemingly would not have made as much of a dent in Gilead itself; indeed, as Commander Putnam revealed, the Republic was very much willing to cut ties with them, leaving nothing but "thoughts and prayers." Now it's those thoughts and prayers that Gilead may need, including the Putnams, as Fred can name names, corroborate stories, and give the International Criminal Court a level of access they have never had before. Will it be enough to bring Gilead down? Perhaps not, because it's already isolated and it can likely only truly fall if there is enough pressure and resistance from within. But it would certainly be a powerful strike: there are already significant restrictions on trading and dealing with Gilead, and the sanctions it faces would likely become even stricter.
As for June, the personal blow to her is every bit as momentous as the geopolitical impact on Gilead. June has survived so much, much of which has been at the hands of the Waterfords. The Handmaid's Tale season 4 is showing how she is struggling to deal with her trauma, with her anger overcoming on her several occasions. That includes at the end of episode 9, where she lunges at Mark and screams "I'll kill you!" It's certainly justifiable in the moment, but the impact this has on June's state of mind could be incredibly damaging. Assuming that Mark does go ahead with the plan rather than changing his mind, then it would mean Fred and Serena walk free, and robbed of that sense of justice, June will struggle even more with adjusting to her new life and the abuses she faced in Gilead. It could be the thing that, as the show has threatened, finally pushes her too far, and could even lead to her seeking out revenge on the Waterfords herself, taking matters into her own hands since the system will not help.