Donald Trump listens to a question during an interview last month in Virginia Beach. (Steve Helber/Associated Press)

The latest Fox News poll is worth examining if only because it might intensify Donald Trump’s meltdown. He trails in the poll by 10 points, the first time he has been trailing Hillary Clinton in any national poll since early July.  In late June, Trump was behind by 6 points in Fox’s poll.

It is also interesting insofar as it sheds light on which issues and constituencies (if any) each candidate is demonstrating progress. The good news for Clinton is that she gained 12 points since June to tie Trump on handling terrorism. Voters consider her qualified by a large margin (65 percent to 35 percent) in contrast with Trump (43 percent to 58 percent). Clinton has also leapt ahead by 10 points with voters lacking a college degree, which used to be Trump’s bailiwick. She is up by 20 points among women and trails among men by just 4 points.

For Trump, the numbers look worse when you isolate Republicans: 30 percent do not think he is trustworthy, 27 percent say he lacks the temperament to be president and 24 percent say he lacks the requisite knowledge. After his convention, he has only 78 percent of Republicans. (Mitt Romney wound up with 93 percent in 2012.) A plurality think his response to the Khans’ appearance at the Democratic National Convention was “out of bounds.” These are Republicans, mind you.

This poll comes at a time state polls in states Trump bragged he could win show Clinton up by substantial margins. Clinton is up by 11 points in Pennsylvania, 17 points in New Hampshire and 9 in Michigan.

Clinton, in short, was helped by her convention and post-convention events; Trump was harmed. How badly Trump was damaged and whether he is capable of repairing the damage remain to be seen.

Bad polls do more than unnerve Trump. They dissuade donors, demoralize potential volunteers and fuel negative news cycles. But they also help Republicans stiffen their spines, as lawmakers who have been on the fence or who need to pull back from Trump will be encouraged as Trump’s support nose-dives. That will likely help swell the ranks of the not-Trump lawmakers (most recently Rep. Adam Kinzinger (R-Ill.), an Air Force veteran who said he cannot back Trump “because he’s crossed so many red lines that a commander in chief or a candidate for commander in chief should never cross.”)

Remember that with the 2014 midterms about two dozen Republican congressmen from states President Obama won or Romney won by less than 10 points entered the House. These Republicans know they need not cling to Trump to win their seats; they have plenty of ticket-splitters. In fact, as Trump gets wackier and his poll numbers sink further, they will have all the more reason to abandon him, and some may even back Clinton as Rep. Richard Hanna (R-N.Y.) recently did.

In the Senate races, both Trump’s declining poll numbers and his refusal to endorse two Republican senators in tough contests — Kelly Ayotte in New Hampshire and John McCain in Arizona — tell other GOP Senate candidates that there is less to be gained by giving Trump even nominal support and much more upside to running as a brake against Clinton’s liberal agenda.

Since, for example, a plurality of Republicans think Trump was out of bounds in attacking the parents of Capt. Humayun Khan, stating one’s objections to Trump in terms of his inexcusable behavior and unfitness as commander in chief may satisfy Republican voters and also take away a Democratic talking point (Congressman X is joined at the hip with the guy who attacked a Gold Star family.)

Polls go up and down. The latest batch, however, coming at a time the Trump campaign is in a tailspin, may bring us closer to a tipping point in the race. As far as Republicans are concerned, it may be the signal finally to jump ship.