Here's the thing, this seems personal...
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If it were JUST about protecting America and the Captain America mantle from a Lukin/Selene/Russian take-over/infiltration, there are less bloody and forceful means of going about it. Yes, I'm a Steve fan, and yes I'm a bit biased when it comes to him, but this... isn't that. Whoever this person is, they have a history with Steve. To the point of overt protectiveness. I'm going 80/20 on this.