LAS VEGAS | When the candidates meet on stage for the first Democratic presidential debate Tuesday, the elephant in the room will be the email scandal looming over front-runner Hillary Rodham Clinton that will tempt her rivals to broach an issue that they so far have avoided, but which remains the biggest vulnerability for her with voters.
The scandal keeps garnering headlines and shaping voters’ opinions despite aggressive moves by Mrs. Clinton and her Democratic allies to bury the issue by denouncing it as a smear job orchestrated by House Republicans and the Select Committee on Benghazi, before which Mrs. Clinton is scheduled to testify next week.
With each passing day, the email controversy grows more difficult to tiptoe around for all the candidates, including Sen. Bernard Sanders of Vermont, who is Mrs. Clinton’s closest competitor, and former Maryland Gov. Martin O’Malley, who is desperately seeking voters’ attention in the race.
“President Obama talked about Clinton’s emails over the weekend, so all of the candidates, including Hillary, need to be prepared to talk about it,” said Craig Varoga, a Democratic campaign strategist who previously worked on President Bill Clinton’s 1996 reelection team and on Mr. O’Malley’s gubernatorial reelection run.
But he warned that using the email scandal against Mrs. Clinton would be risky.
“If one of her Democratic rivals raises it, however, they better be very sure that they do not live in glass houses and don’t have any similar vulnerabilities on either ethics or national security,” said Mr. Varoga. “If they do, the Clinton campaign already knows.”
Neither the Sanders nor the O’Malley campaigns would say whether their candidate intended to raise the email issue.
Mr. Obama delved into the email scandal in an interview aired Sunday on CBS News’ “60 Minutes,” saying that his former secretary of state had made a “mistake” but that she didn’t endanger national security.
“I think she’d be the first to acknowledge that maybe she could have handled the original decision better and the disclosures more quickly,” he said. “I don’t think it posed a national security problem. It was a mistake that she has acknowledged.”
He defended Mrs. Clinton despite an ongoing FBI investigation into her handling of classified material on the private email account that she used exclusively for official business at the State Department. The probe conceivably could lead to criminal charges.
Throughout the campaign, Mr. Sanders and Mr. O’Malley have limited their criticism of Mrs. Clinton to her flip-flopping to adopt more liberal positions, such as her recently coming out in opposition to the Keystone XL oil pipeline and the Trans-Pacific Partnership trade deal.
While Mrs. Clinton’s opponents for the nomination have either taken a neutral position or deferred to the Democratic Party’s anti-Republican rhetoric about the email scandal, voters have taken a harsh view of her conduct.
A poll released this week showed that 71 percent of registered voters nationwide disapproved of Mrs. Clinton’s email practices at the State Department, up from 64 percent who said they felt that way in March.
About 60 percent of voters said they were dissatisfied with Mrs. Clinton’s explanations for it, and just a third said they were satisfied, according to the CBS News poll.
Still, Mrs. Clinton remained the front-runner in the race, leading the next-closest candidate by 19 points.
Mrs. Clinton topped the field with 46 percent, followed by Mr. Sanders with 27 percent, Vice President Joseph R. Biden with 16 percent, former Virginia Sen. Jim Webb with 2 percent and Mr. O’Malley and former Rhode Island Gov. Lincoln Chafee in the bottom with zero support registering in the poll.
When the pollsters excluded Mr. Biden, who has not decided whether to enter the race, Mrs. Clinton’s lead over Mr. Sanders widened to 24 points, 56 percent to 32 percent.
The email scandal also is playing a role as Mr. Biden mulls a third presidential run. He was at home weighing the decision with family over the weekend and is expected to announce his plans as soon as Wednesday.
CNN reserved a podium to give Mr. Biden a spot on stage if he decided to enter the race and participate in the debate.