Support for Democratic presidential front-runner Hillary Clinton has fallen 21-percentage points since July, from 63 percent to 42 percent, based on a new poll conducted jointly by the Washington Post and ABC News.

The former secretary of state, whose campaign has been plagued by lingering questions about her use of a private server for government business, has not effectively managed the uproar about her email habits, 55 percent of Americans said in the survey. A third of Democrats, 58 percent of independents and 83 percent of Republicans also disapproved of her handling of the incident.

While Clinton still leads the field of Democrats, her support has dropped below 50 percent for the first time, the Washington Post noted. The newspaper pointed to her decline among white women, one of her key constituencies, as a critical challenge to her White House aspirations.

Nevertheless, Clinton still is the top choice of 42 percent of Democrats and Democratic-leaning independents, according to the poll, which was conducted between Sept. 7 and Sept. 10, among a random national sample of 1,003 adults, including landline and cellphone respondents, and with a margin of error of plus or minus 3.5-percentage points.

Clinton's closest rival is Independent Vermont Sen. Bernie Sanders, who received the backing of 24 percent, and Vice President Joe Biden, who is still weighing a White House bid as his family continues to cope with the recent death of Biden's son, Beau.

In a hypothetical general election matchup between Clinton and the current GOP frontrunner, Donald Trump, she leads the real-estate tycoon among registered voters by a mere 3-percentage points, indicating a statistical tie. Among all adults, however, her advantage increases to 12 percentage points, the Washington Post pointed out.

Meanwhile, only 39 percent of all voters told the pollsters that Clinton was "honest and trustworthy," while 56 percent said she was not. A majority of Americans also believes that the former first lady does not understand their problems, though 56 percent concede that she has the personality and temperament to serve as president, the Washington Post said.