Irish presidential election front-runner Sean Gallagher is reeling from what he calls a "dirty tricks" campaign mounted by former IRA commander Martin McGuinness.
Seven candidates are standing in the election on Thursday to succeed President Mary McAleese. More than 3.1 million adults are entitled to vote.
Final opinion polls show Mr Gallagher, a television personality and former businessman who is standing as an independent, with a clear lead on 40%. But his advantage is in danger over a row about party donations.
Deputy First Minister McGuinness claimed in a TV debate that Mr Gallagher had accepted a donation of €5000 from a convicted fuel smuggler for his former party.
Mr Gallagher accused Mr McGuinness of dirty tricks over the cheque.
Bookmaker Paddy Power has now installed former arts minister Michael D Higgins as the new favourite. Mr Higgins, 70, was polling at 15% on Monday.
Mr Gallagher spent this week angrily refuting the accusations of wrongdoing by Mr McGuinness.
"I stand over everything I have done as being impeccable with honesty and integrity," he told RTE radio. "I refute any allegations."
The result of the election will probably not be known before Saturday.