The latest surveys look even more ominous for Mrs. Clinton. Virtually all of those taken in the past week show Mr. Trump ahead, tied, or trailing but within the margin of error. The new CNN/ORC poll, out Tuesday, puts Mr. Trump up by two. Rasmussen's release last Thursday showed 40% for Mr. Trump and 39% for Mrs. Clinton. The Reuters/Ipsos tracking poll out Friday had the same figures. The L.A. Times/USC tracking survey shows a statistical tie. The latest Investors Business Daily/TIPP survey has Mrs. Clinton up by one, but the margin of error is 3.4 points.

What accounts for this tightening? On the most straightforward level, it seems that Mrs. Clinton is coming down from the bounce she received after the successful Democratic convention. But something else has changed as well. In the latest ABC/Washington Post poll, published at the end of August, her image hit a career low: 56% of Americans viewed her unfavorably and only 41% favorably. This is a significant slide from even early August, when the same poll had Mrs. Clinton at 52% unfavorable and 46% favorable.

The continuing revelations about her private email server and the business dealings of the Clinton Foundation obviously are taking a toll. The FBI's notes from its interview with Mrs. Clinton, released Friday, reinforce director James Comey's judgment that she was "extremely careless" with classified information. At least 15,000 more emails could be released before November. As for the Clinton Foundation, at this point it is clear that both Hillary and Bill should resign immediately from its board and any role in daily operations.

Meanwhile, Donald Trump has finally begun to focus. Instead of indulging in public spats with other Republicans or the media, he has given speeches on immigration, the economy and terrorism. His image has begun to improve. Barely a month ago Mr. Trump was 30 points underwater in a Bloomberg poll, with 33% of respondents viewing him favorably and 63% unfavorably. Last week's release from Reuters/Ipsos showed 44% favorable and 56% unfavorable.

Still, Mr. Trump has failed to capitalize on two central themes: change and corruption. Fifty-six percent of Americans want to "take the country in a different direction," according to a June poll by YouGov/Huffington Post. And a majority of Americans -- 56% -- think that Mrs. Clinton broke the law by using a private email system, an Associated Press survey found in July. For Mr. Trump, these figures represent a great opportunity.

At the same time, Mrs. Clinton has been struggling to define her own message. Hiding from media scrutiny, she has focused almost exclusively on raising money, hauling in a record $143 million last month for her campaign and the Democratic Party. Her ads targeting Mr. Trump may have done him some damage on the margins. But there is no evidence that they have strengthened her position.

Mrs. Clinton has not offered any defining vision for why she should be elected. She needs an overarching message, beyond simply saying that she is a "change maker," as her husband called her at the Democratic convention. If articulating a substantive vision proves too challenging, it wouldn't be the worst fallback strategy to associate herself with the record of President Obama, whose poll numbers are up, or even her husband. But she's got to do something more than she is currently doing, given her lack of any clear direction for the country and the public sense that she is not trustworthy and arguably corrupt.

So can Donald Trump win? Although he is at a clear disadvantage in the electoral college, evidence suggests that he can. Polls in the past week in Michigan, Wisconsin and Ohio show the race tightening. Florida is within the margin of error. North Carolina and even potentially Arizona, states that once seemed out of reach, remain in play.

In the Midwest, Mr. Trump is surging. The Washington Post/Survey Monkey poll published Tuesday shows him leading by four points in Iowa and three points in Ohio. His path to victory runs through these states, especially with Virginia and Colorado now seemingly safe for Mrs. Clinton. The Midwest is where Mr. Trump should devote the bulk of his time and money, focusing on the need for fundamental change, economic revitalization and empowerment for the disadvantaged -- making his pitch broadly but not exclusively to white working-class voters.

Neither candidate has so far decisively answered the question of who can best lead America into a challenging future, while helping millions of hardworking people improve their lives. If Mr. Trump makes the better sales pitch over the next 60 days, he may very well find himself sitting in the big chair in the Oval Office.

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Mr. Schoen served as a political adviser and pollster for President Bill Clinton, 1994-2000.