For Democrats, a nightmare scenario is looking more and more like a possible reality: Donald Trump is close to even with Hillary Clinton in the presidential polls.

Clinton received a significant bump in the polls following a successful Democratic National Convention and a series of self-inflicted wounds and controversies from the Trump campaign. By Aug. 9, Clinton held an eight point lead and Trump was polling at just under 40 points on average, according to Real Clear Politics. Many pundits declared the race effectively in the bag at that point, but today Clinton's lead is a mere three points. Clinton still has a lead in enough key swing states that she remains the favorite, but a closer look at the most recent polls reveals a few definitive reasons why she cannot seem to pull away from Trump for good.

Here are 5 reasons the polls say Trump could still win:

Stamina

Donald Trump has been branding Hillary Clinton as not having the "stamina" to serve as president for months on the campaign trail, much the same way he shrewdly labeled Republican contenders "low energy" in the primaries. However, a few "alt-right" news organizations, primarily Breitbart and Infowars, took the narrative and ran with it, alleging vast conspiracy theories about Clinton's health, ranging from accusations that certain facial gestures were seizures triggered from a years-old concussion to rumors that a period of somewhat frequent coughing signaled imminent death for the candidate.

Those theories received pseudo-validation when the Clinton campaign revealed earlier this month that the Democratic nominee was suffering from pneumonia. While Clinton has since recovered and her doctors maintain that she is in good overall health — she is one year younger than Trump — the questions surrounding Clinton have seemingly resonated with voters. According to a McClatchy-Marist poll released Friday, 53 percent of likely voters surveyed said Trump has the stamina to be president, while just 39 percent said the same of Clinton. An Economist/YouGov poll released Sept. 19 reached the same conclusion, revealing 37 percent of surveyed voters questioned if she was in good enough physical condition to serve in the White House.

Trustworthiness

Clinton tried unsuccessfully to conceal her pneumonia from voters, unwittingly playing into one of Trump's favorite knocks on Clinton: that she is not trustworthy. From her handling of the 2012 Benghazi embassy attack in Libya as secretary of state, to her use of private email server in office, to questions surrounding access Clinton Foundation donors had to the State Department during her tenure, Clinton has struggled to overcome the characterization that she is, at best, beholden to special interests or, at worst, totally corrupt.

Multiple congressional hearings have exonerated Clinton of any wrongdoing in Benghazi, the FBI has said there was not cause to charge Clinton with a crime over the email scandal and nothing besides surface communication between Clinton Foundation donors and State Department officials has been proven. Yet, the "corrupt" label persists — Trump has referred to Clinton as "Crooked Hillary" on the campaign trail.

Voters have taken notice. Just 36 percent of surveyed voters in the McClatchy-Marist poll said Clinton was honest and trustworthy, compared to 44 for Trump. Meanwhile, the Economist/YouGov poll showed just 29 percent of likely voters found Clinton trustworthy.

Middle Class Values

Trump has positioned himself as the savior of the working class, promising to bring back manufacturing jobs from overseas and cut taxes on the middle class. Whether or not his policies back that up, his candid and, at time, inflammatory rhetoric about the state of the country and the causes of its alleged decline has struck a chord.

Roughly 43 percent of voters in the McClatchy-Marist poll said Trump shares their values, compared to just 41 percent for Clinton. And in an Los Angeles Times/USC poll updated Friday, which shows Trump with a two-point overall lead, nearly 53 percent of voters with an income between $35,000 per year and $75,000 per year (effectively the middle class), support Trump, while just under 39 percent in that same income range support Clinton.

For Clinton to overcome that gap, she will have to prove, perhaps in the upcoming debates, that her economic policies would better bolster the middle class. She will also have to battle the "establishment" label in an election where a majority of voters on both sides of the aisle want to see change in Washington. An NBC/WSJ poll found that 49 percent of voters favor the candidate they believe will bring major course corrections to the way government operates.

White Voters

Critics of Trump argue that his appeals to the working class are not genuine economic appeals, but dog whistles to white voters who fear the impact of minorities and immigrants on their lives. While it could just be correlation, there is data to support the idea.

Trump's reckless rhetoric on immigration and law and order has alienated almost every minority demographic of voters — at one point the GOP nominee was polling at a shocking zero points among African-American voters. However, his support among white voters continues to hold. Trump hold a 60 to 32 point advantage over Clinton among white voters in the LA Times/USC poll, compared to his meager 5-point show of support among black voters and 34 percent support among Latinos.

Clinton obviously benefits from her dominant share of the minority vote, but the Democratic nominee will never score a general election landslide with such a sizeable deficit among white voters. In 2012, President Barack Obama won 39 percent of the white vote over Republican challenger Mitt Romney. However, Clinton's efforts to call Trump's supporters out for racism has led to pushback from voters. More than 50 percent of voters in the Economist/YouGov poll thought she was wrong to say half of Trump's supporters belonged in a "basket of deplorables."

Men

Are American men "ready" for a woman president? Whatever that question means in 2016, the fact remains that Clinton faces an uphill battle when it comes to winning the support of male voters. The Los Angeles Times/USC poll shows her support among men at just under 39 percent to Trump's 50 percent.