Bobby is a tested hero, proven in battle. the biggest mistake they make is testing his mettle. He may hold a soft spot for a certain fluffy telegraph boy, but he is far from soft himself.
He stood with Elias at the sheriff's office in Silver Creek when they were attacked, he led the posse that pursued Cobb into the canyon, he stood at the mine when all was lost, and when Rourke came for Silver Creek itself, he was right by Theo's side keeping the Pinkerton's at bay. Deputy Grady, big ears in a bowler hat he took off of a rogue Pinkerton Agent, defending his Timmy then, like he's doing now.