Who are Ferguson's 'Oath Keepers,' and why are they patrolling the city with guns?

Who are Ferguson's 'Oath Keepers,' and why are they patrolling the city with guns?: "On the one-year anniversary of Michael Brown's shooting death by police, tensions are once again simmering in Ferguson, Missouri. And the arrival of a militia group, known as the "Oath Keepers," threatens to add fuel to the fire in the St. Louis suburb." 

Oath Keepers return to Ferguson, fueling racial tension 'via Blog this'