In Fox's new poll, out Wednesday evening, Clinton had moved up to 44 percent. But Trump had plunged 7 points -- meaning that Clinton now leads the presumptive Republican nominee by 6 points.

As we noted on Wednesday, we should be wary of reading too much into national polls at this point -- or, really, ever -- but there's one bit of data in the Fox poll that seems particularly important. When Democrats were asked whether they preferred Clinton as their party's nominee or Bernie Sanders, Clinton was preferred by 21 points. When Republicans were asked if they wanted Trump or "someone else" -- a majority picked someone else.

That split includes a wide majority of women and of those with a college degree. Remember: This is only among Republicans.

Weakening support from Republicans is almost certainly why Trump has dipped in the polls over the past month. In the Real Clear Politics average of recent polls, Trump has been under 40 percent against Clinton for the past three weeks. If you include Libertarian Gary Johnson in the mix, Trump hasn't been above 40 percent in the average since RCP started calculating the average in the middle of May.

There's only one poll in which Trump has topped 40 percent in a three-way contest against Clinton and Johnson: That May Fox survey.

Using poll data from Huffington Post Pollster, we can show how each major party candidate does with his or her own party. Clinton consistently does better with Democrats than Trump does with Republicans.

She also does better with Republicans than Trump does with Democrats.

You may have noticed in the Real Clear Politics graph above a downward dip for Clinton in recent days. That's thanks to the Quinnipiac and Fox polls, outlined with a box below. (As well as a survey from Republican-leaning Rasmussen Reports.)

The new Fox survey shows a lower level of support for Clinton from Democrats than other recent polls, which combined with increased support from independents for Trump is part of that dip. It's something worth watching over the long term.

The story at the moment, though, is that Republican voters are not terribly enthusiastic about their candidate, with the party's convention looming. We can demonstrate this another way.

Seventy-one percent of Republicans say Trump is "obnoxious." Thirty-seven percent say he's not sensible. Forty-four percent say Trump's not experienced. Only on honesty are Clinton's numbers worse with her own party than Trump's.