After Michael Brown's murder by Darren Wilson, when black people began to assemble and protest, the Ferguson Police Department decided to greet those initial protests with Overhwelming Force. All legitimate complaints about excessive force, ticky-tack violations, and unconstitutional Stop & Frisk met a literal wall of riot shields and machine guns mounted on military surplus vehicles.
Of course, the complaints of the protesters were vindicated by the Department of Justice Report on the shoddy Police practices of the Ferguson PD which was based on the revenue generating Broken Windows Theory which treats every Person of Color as a potential criminal.
Much like their sister organizations the Unconstitutional Sheriff's of America, the III Inchers errr, Percenters, and the various unaligned Soverign Citizens, the Oathbreakers represent the Re-rise of the Anti-Government Militia Movement in the United States.
In his seminal 1962, SE Finer, in his seminal 1962 book The Man on Horseback: The Role of the Military in Politics, described the underlying mindset which fuels the Oathbreakers,
"I find in existence a new and heretofore unknown and dangerous concept that the members of our armed forces owe primary allegiance or loyalty to those who temporarily exercise the authority of the Executive Branch of Government rather than to the country and its constitution which they are sworn to defend."
No proposition, added General MacArthur, 'could be more dangerous.' On the contrary, it is General MacArthur's view which opens Pandora's Box. The moment the military draw this distinction between nation and the government in power, the begin to invent their own private notion of the national interest, and from this it is only a skip to the constrained substitution of this view for that of the civilian government. ( ibid. pg 22-23)Finer used a quote from General Douglas MacArthur in 1952, who was in a power struggle with President Harry Truman, which famously led to MacArthur's removal as Commanding General during the Korean Conflict.
Like most of the Reactionary Conservatives who make up the American Right today the Oathbreakers are a lily white group who have convinced themselves that the only legitimate government is one which hews closely to their "understanding" and interpretation of the Holy Constitution.