The Dáil resumes its debate on the Flood tribunal report this afternoon, with the Taoiseach expected to explain in more detail his appointment of Mr Ray Burke to the Cabinet in 1997.
Yesterday, Mr Ahern said he would not have appointed Mr Burke if he knew then what he knows now.
"It is five years later, and my decision at the time was a bona fide one based on Mr Burke's undisputed political abilities, his categorical assurance that he had done nothing wrong, and a number of inquiries," Mr Ahern said.
The Tánaiste, Ms Harney, last night defended her decision to support the appointment of Mr Burke.
But Fine Gael leader Mr Enda Kenny said the Taoiseach has brought the "highest political office in the land into the lowest-possible public repute".
Labour deputy leader Mr Brendan Howlin said the reality was that the "Tánaiste's knowledge of the existence and seriousness of the allegations against Mr Burke was considerable".