Presidential candidate Hillary Clinton finally apologized for her use of a private email server while secretary of state in an interview with ABC on Tuesday.

"That was a mistake," Clinton said. "I'm sorry about that, I take responsibility, and I'm trying to be as transparent as I possibly can."

The clip was an excerpt from an interview with ABC World News Tonight anchor David Muir, which is slated to broadcast in full Tuesday night. It marks a major change in rhetoric for Clinton, who has been adamant that nothing she did regarding her use of a private server merited an apology.

In that time, her polling has suffered among voters across the political spectrum. The Democratic nomination that once seemed to be hers is now in doubt as Sen. Bernie Sanders (I., Vt.) surges in the early primary states of Iowa and New Hampshire and Vice President Joe Biden mulls a potential run for the White House as well.

This admonition came just 24 hours after she told the Associated Press that she had no need to apologize for her private, unsecured server that contained classified information, saying "what I did was allowed."

Asked Monday by the AP why she won't directly apologize, Clinton said: "What I did was allowed. It was allowed by the State Department. The State Department has confirmed that. I did not send or receive any information marked classified," Clinton said. "I take the responsibilities of handling classified materials very seriously and did so."

On Friday, Clinton was asked twice by MSNBC's Andrea Mitchell if she was "sorry" for he conduct, but both times Clinton maintained that, while she wished she made a different choice, her server was allowed and fully "aboveboard." Mitchell and other pundits noted afterward that Clinton refused to apologize.