I hope CA3 involves the replacement Captain America. The writer(s) can update and merge the backstories of John Walker and the ‘Anti-Cap’. John Walker can start off as a 21-ish year old enlisted man, dishonorably discharged after a 3-year stint in the Navy on September 10th 2001 (he was part of a weekend-pass/voucher forging operation). His girlfriend, who had recently quit him, was an intern working in the WTC). Back in his Georgia hometown, Walker is heartbroken, despondent, and rage-filled, he is turned down for reenlistment. He drifts from job to job, usually getting fired after blowing up at someone. 6 months later, he’s embedded with a militia group that’s involved in a plot to blow up a local bridge. As it turns out, the group has been infiltrated by an FBI agent; the agent offers Walker immunity for his cooperation. Walker reluctantly complies, and is in turn confronted by a Navy admiral, who offers him a chance to ‘redeem himself for his country’. Thus does Walker become the volunteer for the ‘super-SEAL’ program. An alternative to the original serum is used, with modern steroids. The ‘US Agent’ was not publicized, a wetwork operative. He has been active throughout the years. When Steve publcly quits SHIELD for a time, Walker is brought in publicly. A new sidekick is brought in (Battlestar). A new villain can be Alexander Lukin, the Kronos corporation. Other options include Dr. Faustus, Cobra, Flag Smasher, etc. I would have Steve become Nomad while he was replaced, then go on his own against the bad guys, eventually coming to blows with USAgent/Anti-Cap and the main villain at the same time.