WARNING: The following contains minor spoilers for The Falcon and the Winter Soldier Episode 5, "Truth," now streaming on Disney+.
John Walker's life has fallen apart spectacularly in The Falcon and the Winter Soldier. After his introduction as a war hero who wanted to do right by the name Captain America, he has made several poor decisions.
John Walker lost his rank completely after he murdered a man in public. In the fifth episode, "Truth," he faced what amounted to a court-martial and lost everything. This is very similar to what happened in the comics, but is slightly different when it came to the sins of the new Captain America.
John Walker got his start in comics when he took on the role of Super-Patriot. Much like on The Falcon and the Winter Soldier, he was a member of the U.S. Army before this. However, unlike the TV show, he was never a war hero. His brother Mike was the hero, and John patterned his life after the memories of his older sibling, although he later learned the stories were not as true as he had remembered. After leaving the Army, he met a man known as the Power-Broker and underwent a process giving him superhuman powers. After John tried to prove he was more worthy than Captain America, the U.S Government eventually gave him a chance to prove himself when Steve Rogers gave up the mantle.
John Walker took on the role in Captain America #333 by Mark Gruenwald and Tom Morgan. He even got his own sidekick in Lemar Hoskins, who became Battlestar. Things looked good at first, but John had a different mindset than Steve Rogers. He was a little more rough-around-the-edges, and he often let his emotions get the better of him. Things went wrong quickly when two of his old partners that he was forced to drop due to lack of security clearance betrayed him by revealing his real name to the world in Captain America #341 by Mark Gruenwald and Kieron Dwyer. This simple action came with dire consequences.
John's first mission as Captain America had him targeting a hate group called the Watchdogs, a racist group that killed anyone they felt did not stand up to the ideals of their vision of America. While John agreed with many of the hate group's stances, he still did his job. Sadly, when the Watchdogs got news of John's identity, they murdered his parents. That was all it took for John to lose himself completely. John killed a dozen of the Watchdogs, which set the Commission in motion to consider stripping him of the Captain America title. He hunted down his former friends who caused his parent's death, tied them up, and blew them up. Both men lived but ended up in comas. It was this action that caused the Commission to finally put an end to John Walker's role as Captain America.
Much like in The Falcon and the Winter Soldier, there was a formal court-martial. The Commission stripped John of his rank and title, returning it to Steve Rogers. John even asked Steve to take it back to keep the Commission from assigning someone else to the role. After a faked assassination, John Walker returned as U.S. Agent with his secret identity returned and set out to find redemption by joining the West Coast Avengers.