Hillary Clinton’s unfavorability rating has hit a record high as the former secretary of state pushes to become the Democratic nomination for president, a campaign that has been weighed down by inquiries surrounding her use of private, unsecured email at the State Department.

Currently, 55 percent of American voters view Clinton unfavorably, according to a CNN/ORC poll released Tuesday that was conducted in the days leading up to the Democratic primary in South Carolina, which Clinton won over the weekend. This represents the highest unfavorable rating that Clinton has registered in the history of the poll, which has asked the question since March 1992.

The share of Americans viewing Clinton negatively has ticket up three percentage points in the last month as reports have continued to emerge about the presence of classified information on Clinton’s private server, a controversy that has been brewing for nearly a year.

More than 2,000 Clinton emails that the State Department has released to the public under court order contain classified information, though the agency and Clinton’s campaign have insisted that the correspondences were not marked classified when they originated on her email. Twenty-two messages have been upgraded to top secret, and those were blocked from release because of their high sensitivity.

Clinton’s unfavorable rating increased to 53 percent in August 2015 in the days after Clinton handed her email server over to the Department of Justice. The FBI has since been investigating Clinton’s email setup. Critics have consistently argued that Clinton put national security at risk by using an unsecured email to conduct sensitive government business.

The former secretary of state’s unfavorable score had never been higher than 53 percent before the latest poll, and it dipped as low as 22 percent in early 1993 at the start of her husband Bill Clinton’s presidency and the beginning of her stint as first lady.

The survey also indicates that Hillary Clinton’s favorable rating is her lowest in more than two decades. Currently, 42 percent of Americans view the former secretary of state positively. It hovered below 40 percent only in the early months of 1992, when about a third of voters didn’t know enough about her to form an opinion.

The new poll was released on March 1, also known as Super Tuesday, when voters in a dozen states headed to the polls to cast ballots in the Democratic and Republican presidential primaries. Clinton has faced an unexpectedly strong challenge from Sen. Bernie Sanders (I., Vt.) for the nomination, though she is still widely viewed as the frontrunner.