But this is one poll, and we don't get excited about the top-line numbers from one poll, because we are not the Hill. As Nate Silver put it on Twitter, recent polls have been "a cherrypicker's delight," since some (like the Los Angeles Times/USC poll) have showed a close race and others, like this one, have shown a less-close one.
In the RealClearPolitics average of recent polls, Clinton's back to a six-point lead, in the range where she's been since shortly after the conventions.
(RealClearPolitics hasn't incorporated another new poll just out from PRRI, which shows Clinton up by 13 points.)
What we can learn from the Quinnipiac poll is what's changed since their last survey, conducted at the end of June. In that poll Clinton led 42 to 40. Now, she leads 51 to 41.
As a result, plotting the margins of support for Clinton over Trump by demographic, most of them have shifted to the left — meaning that the margin by which Clinton leads has grown or the margin by which Trump leads has shrunk.
We see that this holds true by party. In June, 6 percent of Republicans said they'd back Clinton; that jumped to 12 percent. The percent saying they'd back Trump didn't move.
Interestingly, Trump saw an erosion of support from white men but not white women (who already favored Clinton). Overall, Trump leads with whites by 11 points (down from 13 in June) and trails among nonwhites by 62 points. Overall, Clinton's lead with women increased by seven points, and Trump's lead with men shrank by the same amount.
The oldest and youngest voters were the ones who moved the most toward Clinton, by 12 and 10 points respectively.
But why did Trump's support slip? Well, at the same time that Clinton's margin in the polls grew by eight points, Clinton's net favorability (those who view her favorably minus those who view her unfavorably) grew by eight points as Trump's fell by five. More than half of voters now say they have a strongly unfavorable view of the businessman — not the direction he'd want to go.
President Obama is viewed favorably by 54 percent of respondents, a good sign for Clinton.
The pollsters also asked whether respondents felt that Trump's campaign rhetoric appeals to bigotry. Well over half, 59 percent, said that it did. Even worse for Trump, a plurality of every demographic save Republicans felt that he appealed to bigotry, including majorities of independents, men, women, whites with or without college degrees, people aged 64 or younger and both whites and nonwhites. Among all whites, 54 percent felt that Trump appeals to bigotry (with 50 percent of white men agreeing). Among nonwhites, the figure was 72 percent. (With 29 percent of Republicans saying they think he appeals to bigotry and 84 percent supporting him, that means that at least 13 percent of Republicans both think he appeals to bigotry and plan to give him their vote.)
Interestingly, Trump is seen as more honest than Clinton in this poll. That's unusual; most polls show them at about the same level. But Clinton makes up for that by being seen as more experienced, levelheaded and qualified — by big margins (39, 37 and 26 points, respectively). More than half of respondents said that, no, those terms don't apply to Trump in each case.
Trump has hinged his election on being seen as a change agent. And, sure enough, 46 percent figure that things wouldn't change much if Clinton wins the presidency. But 46 percent of respondents think that the change Trump would bring is the wrong change, which isn't really the framing Trump would like to see.
If nothing else, the story of this poll should be that even several weeks after they ended, Trump hasn't done much to shift the way the conventions set the race. This poll shows a bigger gap than most but most polls show a gap in her favor to some extent. The details of the new poll show why: Trump simply isn't seen as presidential material by most Americans.
Clinton's Brooklyn team will probably be giddy about that, too.