By now, it's far too late for Donald Trump to be anyone but Donald Trump. It was probably too late back in July, when he accepted the nomination, and it was probably even too late in May, when he won it.

It was probably too late before voting began.

In March, Bloomberg Politics asked Republican primary voters who had the better temperament to be president: Trump or Sen. Ted Cruz (R-Tex.). There was no question: By a more than 2-to-1 margin, Republicans said Cruz was their choice in that regard. Only 27 percent of respondents thought Trump's temperament was better.

On Wednesday, with the third and final general-election presidential debate looming, Bloomberg asked the same question, this time about Trump and Hillary Clinton. Nearly 60 percent of likely voters said that Clinton had the better temperament. Trump was again preferred by 27 percent of respondents.

Since The Washington Post and our partners at ABC News began asking about the qualifications and temperament of the 2016 major-party candidates, Trump has never been viewed as qualified by more than 41 percent of Americans, and no more than 35 percent have said he has the proper temperament for the job. Clinton has never been below 56 percent on either metric.

Those things are linked. Last month, Quinnipiac University asked those who viewed Trump as unqualified why they viewed him that way. The most common response was his temperament.

Fox News asked the same question in its poll released Tuesday night. Among nearly every demographic group, a greater percentage viewed Clinton as having the right temperament to be president than those who viewed Trump that way. The exceptions? Trump's core of support: White Republican men without college degrees.

Only about two-thirds of Republicans viewed Trump as having the right temperament, though, vs. 94 percent of Democrats who said the same about Clinton. Only among white men without degrees did a majority say that Trump had the proper temperament.

Overall, 61 percent of respondents said Clinton had the right temperament. Thirty-five percent said that was true for Trump.

When Fox asked the same thing in April, the figures were almost exactly the same. Trump, 33 percent. Clinton, 61.

Donald Trump has been running for president for 490 days. Over that period, he has been the subject of thousands of interviews, given scores of speeches, made his case repeatedly. A perception that he is not temperamentally fit for the job has not budged an inch. Even after two debates — maybe because of those two debates — Trump is viewed unfavorably on this metric.

There is nothing Trump can do in the last debate or in the final 20 days to change that.