Donald Trump's address to supporters in Phoenix was "downright scary" and called into question the President's fitness to lead, according to a former top US intelligence official.
James Clapper, the former Director of National Intelligence, said he also thought Mr Trump's divisive remarks showed he might be "looking for a way out" of the office. He criticised what he called the "complete intellectual, moral and ethical void the President of the United States exhibits".
Mr Trump's sometimes venomous speech in Arizona took aim at the "crooked media" and both the state's Republican senators, Jeff Flake and John McCain, with whom he has clashed previously.
He blamed the media for widespread condemnation of his response to deadly violence at a white supremacists' protest in Charlottesville, Virginia, shouting that he had "openly called for healing, unity and love" after the tragedy and had been misrepresented in news coverage.
Mr Clapper, 76, told CNN's Don Lemon: "I've toiled in one capacity or another for every President since and including John F Kennedy through President Obama, and I don't know when I've listened and watched something like this from a President that I found more disturbing.
"Having some understanding of the levers of power that are available to a President, if he chooses to exercise them, I found this downright scary and disturbing.
"I really question his ... fitness to be in this office, and I also am beginning to wonder about his motivation. Maybe he is looking for a way out."
Mr Trump's ability to use nuclear weapons if he deemed it necessary was a particular concern, he added.
Mr Clapper left office on 20 January, when Mr Trump was inaugurated.
Mr Trump opened his speech, at the Phoenix Convention Centre, with calls for unity and an assertion that "our movement is a movement built on love". But he later abandoned his teleprompters and grew angry as he criticised the "damned dishonest" journalists he said had misrepresented him.
He revisited his various statements in the wake of the violence far-right rally in Charlottesville, reading them back to prove he had condemned white supremacists, but omitting the sections in which he blamed "both sides" or "many sides" for the outbreak of violence.
"You know where my heart is," he told the thousands of supporters who had braved searing temperatures to attend.
Mr Clapper, who appeared downcast and sombre during his interview, added: "I do wonder as well about the people who are attracted to this rally, as others. What are they thinking? Why am I so far off base? Because I don't understand the adulation.
"He should have quit while he was ahead after [his teleprompter-based Afghanistan speech] last night, but again I think the real Trump came through.
"The key thing here is, where is he with Republicans? I was quite struck by Senator Corker's remarks. Very thoughtful and very measured. I'm hopeful that other, similarly thoughtful Republicans, will reach the point where enough is enough."
Mr Corker, a senator from Tennessee, said earlier this week that Mr Trump "has not yet been able to demonstrate the stability nor some of the competence that he needs to demonstrate in order to be successful," CNN reported.
He urged Mr Trump to do "what is necessary" to show that "he understands the character of our nation and works daily to bring out the best of the people in our nation".