The Taoiseach has accused Sinn Féin of being "soft on crime and high on taxes".
A leaders' debate between seven political party leaders is taking place at NUI Galway tonight.
It is the first opportunity Sinn Féin leader Mary Lou McDonald has had to debate with both Leo Varadkar and Fianna Fáil leader Micheál Martin.
Both party leaders have ruled out going into a coalition with Sinn Féin.
The Taoiseach said the decision is not personal, but is "entirely based on policy and principles".
He said: "The reason why my party wouldn't be in a position to form a coalition with Sinn Féin is that in our view, Sinn Féin is soft on crime and high on taxes."
He also cited Sinn Féin's proposal to remove the Special Criminal Court as a reason for his party's reluctance to form a potential government with them.
This stance was shared by Micheál Martin.
Also in attendance at tonight's debate is Labour leader Brendan Howlin and Eamon Ryan from the Greens.
Richard Boyd Barrett is flying the flag for Solidarity-People Before Profit, while the Social Democrats is represented by co-leader Roisin Shorthall.
Some of the issues discussed during the debate were those dominating the General Election so far, including housing, homelessness, health and climate change.
Meanwhile, several Aontú supporters are holding a protest outside NUI Galway this evening.
It comes after the newly formed party was excluded from tonight's debate.
Earlier, Aontú withdrew its legal application in the High Court in relation to the debate, claiming a lack of time to process the required paperwork.
