Sebastian Gorka, the deputy assistant to the US President, has become the latest to depart from the White House, according to reports.
Gorka wrote in a resignation letter that those who were most closely aligned with Donald Trump's agenda were being culled.
However, the White House disputes the claim that Gorka resigned, and has instead implied he was fired.
In the resignation letter seen by Politico, Gorka wrote: "Regrettably, outside of yourself, the individuals who most embodied and represented the policies that will 'Make America Great Again' have been internally countered, systematically removed, or undermined in recent months."
It is thought Gorka, a Bannon ally, argued with national security adviser General H.R. McMaster.
A White House official said in a statement:
Sebastian Gorka did not resign, but I can confirm he no longer works at the White House.