Democratic presidential candidate Kamala Harris referred to her presidential rival Donald Trump as "increasingly unhinged and unstable" on Wednesday, over responding to John Kelly's comments about Trump's fascist aspirations.

“I believe Donald Trump is a danger to the well-being and security of the United States of America,” said Harris. She has time and again expressed her worry about Trump's mental fitness for running the state as president. 

She spoke outside her residence in Washington after Trump's former presidential chief of staff, retired Marine general John Kelly, went public with revelations about the Republican's admiration for the Nazi dictator and his military in World War II.

"It's deeply troubling and incredibly dangerous that Donald Trump would invoke Adolf Hitler, the man who is responsible for the deaths of six million Jews and hundreds of thousands of Americans," Harris said before leaving for a televised town hall in swing state Pennsylvania.

"All this is further evidence for the American people of who Donald Trump really is."

Kelly told The New York Times that Trump had remarked that "Hitler did some good things too" and that instead of the US military he "wanted generals like Adolf Hitler had."

Kelly also repeated his warning that he believes his ex-boss "certainly falls into the general definition of fascist."

Harris said "Donald Trump is increasingly unhinged and unstable, and in a second term, people like John Kelly would not be there to be the guardrails against his propensities and his actions."

"So the bottom line is this: We know what Donald Trump wants. He wants unchecked power," Harris added, warning that Trump wanted a military that "is loyal to him" and not to the US constitution.