Omarosa is blasting Donald Trump for having the audacity to claim illegal immigrants are taking away "Black jobs" ... and says he owes voters some explanation for what he meant.

Trump's former 'Apprentice' ally tells TMZ ... his remarks at the debate about "Black jobs" and "Hispanic jobs" were totally insane. Like millions of people watching Thursday night, she says she was left wondering what exactly those terms signify to the former president.

As far as Omarosa is concerned, the only exclusively Black job she can remember in America is slavery ... which has her thinking Trump might have let some racism slip there by throwing it back 400 years.

Remember, one of the lowlights from Thursday's debate was Trump ranting about illegals taking away jobs ... but, in true Trump fashion, he pissed off a lot of folks with his choice of words around the topic. Although his backers would say he was simply playing to his base.

Omarosa isn't mincing words, however, calling Trump a racist ... and citing some old reports about his hiring practices at his failed casinos as evidence.

Of course, she has a long history working with Trump -- from "The Apprentice" to the White House -- and knows him well.

No matter what Trump meant, Omarosa says African-American and Hispanic voters are not monolithic ... and each person should vote for the candidate that best suits their individual needs.

Still, she wants Trump to clear up the confusion here ... or at least have someone from his campaign set the record straight.

As for the debate as a whole, Omarosa says Trump was showing signs of mental decline and neurological issues ... and she thinks people forget about that when they focus on Biden's age and mental capacity.

On style points alone, Omarosa is giving this round to Trump ... but when it comes to substance, she says Biden's the clear winner.

Omarosa's got lots to say here ... and she tells us who she's voting for in November and why.