In the year 200011:
The Ferry fell, and finally took "peacetime" and all associate illusions of how the the world was working out with it. Having foreseen (and even wanted) war as an (unfortunate) inevitability from the start, Calvin should've been in a good position to take full advantage, rising up, leading the way, riding the wave of revolution.
It didn't really work out that way.
Something Calvin hadn't wanted or foreseen was the fall of the Ferry, embarrassing as they could be.
Further, he was in a state of institution in their basement when they fell, and had been for a month or two — captured with Bella's assistance and held behind bars and under negation to protect him from himself. Also to protect the rest of the world from himself. He'd been increasingly mentally unstable for months, caught up in a state of perpetual near panic at the sheer magnitude of the crimes he was committing, uncertainty about the direction he was moving in, guilt over past indiscretions, and so on, held together by the force of his own personality and the knowledge that he was ultimately in the right — willing to take steps no one else had the fortitude to in pursuit of a greater good. Sacrificing his own reputation and soul so that the others he traveled back with wouldn't have to.
So apart from having plenty of time alone to chill out and find perspective, he still wasn't in the greatest shape psychologically when Benji came to fetch him the night of the final assault on Pollepel.
What the fall (and the war) gave him was a reason to realign more closely with Benji as a stabilizing influence, even if it was at arm's length. Calvin gained a ballast against insanity with his (mostly) best interests in mind, and Benji gained Calvin as a war asset. The destructive force of his ability combined with his distinctive appearance and extreme approach quickly solidified his reputation as someone you wouldn't want to see turn up on the battlefield. It also made him something that more good and lawful leaders operating against Mitchell weren't always eager to partner with. Where distinctions might be made between warfare and terrorism, he was weighted heavily towards the latter, favouring shock and awe over fair play.
He and Benji became ambush predators in warzones — wildcard allies that sometimes coordinated with more organized efforts but just as often sort of showed up. They built up a level of Bonnie and Clyde style infamy, where they were well-known as a help to the evolved cause but (Calvin especially) never widely regarded as Heroes, save maybe by other extremists and maybe eventually edgy teenagers. Benji was a more quiet and elusive shadow traveling with him. She was less an open combatant, and certainly less contentious in reputation despite the altogether more insidious and terrifying aspects of her ability when applied as a weapon.
They might have attracted a troop of like-minded evos during this time — individuals a little too bloody-minded or undisciplined to hang with the military or former Ferry crowd, but ready and willing to take risks to deal damage. There wouldn't have been any formal leadership, and casualties would have been common. Calvin was of a more strategic mind than most of them, and would have acted as a representative where it was unwieldy or unwise to have Benji work as a go-between. This isn’t/wasn’t a faction so much as just a loose knit group of people who worked together and may work together again.
Calvin was in Washington state when the nukes went off, although not directly involved in the attempts to stop them.
He immediately shifted his focus onto picking apart enemy troops in the area that were disabled or otherwise hindered by the blast like a hawk on half-dead roadkill.
In the years immediately following the war, he stuck to the west coast for a while and assisted — a bit — with recovery — with getting people and important assets out of the dead zones. He saw a lot of fucked up shit in this time — people affected by the bomb that dropped on Portland, and the like. There was some confusion there, in his black heart of hearts, over the war being "won" on paper — but not really feeling won. Probably worse for the world at large, he knew Benji felt the same way.
Like maybe team Mitchell hadn't really suffered enough for what they'd done — maybe they hadn't really gotten the message, or been ground far enough down into the dirt to assure that they'd never rise up again.
A snap decision to execute one of Mitchell's military minds while he was being transported out of Seattle in police custody in early 2015 for a hearing is where Calvin officially shat the 'reintegrating into society' bed.
Ever since, he's been collaborating closely with Benji and other lingering extremist minds to track down and murder remaining members of Team Mitchell, including some that the law was unable to find guilty, or cut deals with in exchange for their cooperation (former Company and Institute employees, etc). This will likely have included snatching (or attempting to snatch) captives from the jaws of Wolfhound and other government/government sanctioned agencies to dispense a more brutal brand of justice, aided by intel gleaned by Benji. He will have been a thorn in the side of anyone trying to do things the right way, and is now wanted himself, for murder, among other things.
BECAUSE he's so visually distinct, he cannot use public transport, or risk entering cities or regions "up and running" enough that they'd be capable of scrambling to capture him. As such, he tends to hang around cities that are dense with ruin that he can retreat into, or so disorganized that their police or militia wouldn't bother with getting themselves killed trying to run him down.
I'm thinking someone might have had a very serious go at him in during a stay in California in the last year — maybe a near capture. Suspicious of a mole within his contacts in Cali, he broke off the mission and travelled all the way across the country back to Benji in NYC to force anyone on his trail to start over from scratch.