Heidi Przybyla, USA TODAY 5:59 p.m. EDT August 30, 2015

Hillary Clinton speaks at the Democratic National Committee summer meeting on Aug. 28, 2015, in Minneapolis.(Photo: Adam Bettcher, Getty Images)

August can be the cruelest month of the year for Democratic presidential candidates. Just ask Hillary Clinton.

The Democratic presidential front-runner's favorable rating is down to 39% in a recent Quinnipiac poll, from as high as 48% earlier this year. A Des Moines Register/Bloomberg Politics Iowa Poll released Saturday showed her lead over Vermont Sen. Bernie Sanders down to seven points in the state that hosts the first caucus early next year.

It's a month that's been unkind to other Democrats, too. In August a year before his re-election, President Obama’s approval rating stood at 40%, the low point of his presidency, according to Gallup; the same month in 1995, Clinton's husband, Bill Clinton, was at 46%, 12 points lower than shortly after he was re-elected.

Much of the handwringing in the Democratic Party is over the 61% of Americans who now say Clinton is not honest and trustworthy. It’s evidence of the damage done by a drumbeat of summertime stories about whether she sent and received classified material over her private email server as secretary of State.

"It’s important that she manage this,’’ GOP pollster David Winston said. "But it’s way too early to be talking about death knells.’’

In August 1996, months before they re-elected him, 51% of Americans also said Bill Clinton, was not honest and trustworthy. To be sure, he had advantages she will not, including a thriving economy and voter backlash to a Republican-driven government shutdown.

"It’s quite a testimony to the fact that trustworthiness is not the only dimension in which voters think about a presidential candidate,’’ said Evans Witt, a non-partisan pollster and chief executive of Princeton Survey Research Associates International, noting as well how long it still is until the 2016 general election.

It's a long view of the former first lady’s polling data that explains why it'll take far more adversity before Clinton and her allies sense real danger. As the email controversy drags on, her unfavorable ratings could dial further upward. That’s particularly true as the summer comes to a close, voter interest in the election perks up and Republicans prepare to grill her before a House special committee on Benghazi on Oct. 22.

One could also derive inauspicious signs from her current favorability numbers given that both Bill Clinton and Obama stayed above 50% the year before they were re-elected. Most political experts hold that it’s difficult for any presidential candidate to win with a number much below that. Yet, in the current anti-Washington political climate, none of the 2016 candidates cross that threshold, according to Quinnipiac. To boot, several are already in negative territory, including Jeb Bush, Ted Cruz, Rand Paul and Donald Trump, who, despite leading GOP polls, has the highest unfavorable rating of all at 54%.

Much of the decline in Clinton’s favorability comes from people who would never vote for her anyway — Republicans and Republican-leaning voters who identify as independent, Witt says. There’s been an average 12-point increase among Republicans and independents.

Among Democrats, her numbers haven’t changed much. From March — before she officially announced her campaign and when her use of the private email account first surfaced — through August, Quinnipiac found her unfavorable rating increased from six to 11%.

"What you’re seeing is, well, Republicans don’t like her,’’ Witt said. As Clinton served as the nation’s top diplomat, Republican attitudes about her warmed, pushing her ratings as high as 62%. Now, however, she’s back in the political arena where opinions are more polarized.

"There was a period of several years as secretary of State where she was extremely popular by a large margin,’’ Democratic pollster Mark Mellman said. "That was bound to change when she became a candidate.’’

What may matter most is how Clinton ranks relative to her Republican competitors, who’ve yet to face the same intensity of scrutiny.

Right now, she’s still either ahead of or within the margin of error vis-a-vis Trump, Bush and Marco Rubio, three of the GOP's top performing candidates.

Follow @HeidiPrzybyla on Twitter

Read or Share this story: http://usat.ly/1EtMvQN