Fox asked respondents whom they'd pick in a head-to-head matchup or a three-way contest including Libertarian Gary Johnson. Running only against Trump, Clinton led by 10 points. With Johnson in the mix, she led by nine points, with Johnson pulling from both candidates about evenly.

The support for each candidate comes from the by-now-expected demographics. Clinton leads with women by 23 points; Trump leads with men by five. Clinton leads with black voters by 83 points (!); Trump leads with whites by 10. Of note: Clinton trails with independents by eight points, but gets 12 percent of the Republican vote to 5 percent of Democrats who say they'll back Trump.

The average of recent polls shows a clear separation for Clinton after the conventions, with Trump's post-convention peak quickly evaporating.

A big chunk of each candidate's support comes from people who want to see the other person lose, but, as with the CNN-ORC poll released this week, Clinton's support is more heavily from people who want her to win. Trump's is more heavily from people who want Clinton to lose.

Some of the starkest differences are found in perceptions of each candidate's fitness for office. Neither Clinton nor Trump is seen as particularly honest; only about a third of the electorate sees either that way. But Clinton has huge advantages on temperament, qualifications and knowledge for the job.

The poll was in the field as the controversy over Trump's response to the family of Army Capt. Humayun Khan was raging. A staggering 69 percent of those who were familiar with the issue thought Trump's response was out of bounds, including pluralities of every single demographic group — even Republicans.

Unlike that CNN-ORC poll, Trump is still seen as the better candidate on economic issues, the issue that respondents in the Fox News poll ranked as the most important.

But that's clearly not enough to get a majority of them to back his candidacy.