Just a really bad, stupid, implausible movie
That is all.
"Love isn't what you say or how you feel, it's what you DO". (The Last Kiss)
Why would the head of a huge white supremist organisation that had the resources to make the Federal Marshal Service look silly, as well as hire highly professional assassins left, right and centre, personally go out and shoot the local shopkeeper and his son.
Why would the Marshal Service operate out of what looks like a hire storage facility?
Why was there no security there at all? It's supposedly there to assist with witness protection, yet it appears people are just able to walk in and walk out as they please.