FIANNA Fail leader Micheal Martin launched a scathing attack on Sinn Fein as he concluded his party's two-day think-in.
Mr Martin was responding to weekend comments made by Northern Ireland's Deputy First Minister Martin McGuinness when he said Sinn Fein is aiming to overtake Fianna Fail electorally.
But Mr Martin angrily slammed Sinn Fein's performance in the Northern Ireland Executive as "dysfunctional" and said he isn't concerned.
He said: "Fianna Fail's focus is on the people of Ireland, it's not playing political games.
"I don't look over my shoulder. We as a political party exist to develop policies, programmes and core values that can be of value to the Irish people.
"Others certainly, like Martin McGuinness, can look over their shoulders at us, that's their business. I'm not going to be shaped or influenced by the machinations of other political parties or what they are about."
His attack on Mr McGuinness comes as speculation mounted that the Sinn Fein leader in the Northern Executive could be the party's candidate for the presidential election.
Sinn Fein is determined to enter the presidential race in an effort to trump Fianna Fail, which has decided it should not contest the election.
The former Minister for Foreign Affairs said he had first hand experience of how poorly Sinn Fein had performed in the Northern Ireland Executive.
He said: "Just look at Sinn Fein's performance in government in Northern Ireland, it's been pretty poor in terms of their executive responsibilities.
"The Northern Ireland Executive, unfortunately, had been dysfunctional for too long because of the quality of the input of parties like Sinn Fein.
"I had experience of this as Foreign Affairs Minister, when I was involved in devolution of justice, for example.
"When you're a political party you have to act like a political party. It's not just about winning seats and numbers."
The former minister spoke out during a press conference to conclude Fianna Fail's think-in which took place to discuss a strategy for the new Dail session, which begins today.