Sinn Fein leader Mary Lou McDonald has struggled to explain how her party would finance a multi-billion-euro giveaway.
Ms McDonald also floundered when questioned last night about her party's links to the Provisional IRA and in particular its treatment of the family of murdered Paul Quinn.
She refused to ask her finance minister in the Northern Assembly, Conor Murphy, to apologise to Mr Quinn's grieving mother for suggesting he was involved in criminality.
An IRA gang are believed to be behind the brutal killing of the 21-year-old in Monaghan in 2007. Every bone in his body was broken after he was lured to a shed near Castleblayney.
Last night, Briege Quinn pleaded with voters: "I'm saying to the people: remember Paul Quinn when you are marking your X."
However the latest opinion poll shows support for Sinn Fein is continuing to rise and they are now the most popular political party in the country. Ms McDonald is also the country's most popular leader five days out from the General Election.
The 'Irish Times'/Ipsos MRBI poll has Sinn Fein up four points to 25pc while Ms McDonald's personal satisfaction rating is up seven points to 41pc.
Meanwhile, Fine Gael is down three to 20pc and Fianna Fail has dropped two points to 23pc. Taoiseach Leo Varadkar and Fianna Fail leader Micheal Martin's personal ratings are both at 30pc.
The Green Party are unchanged at 8pc and the Labour Party are down one to 4pc. Solidarity-People Before Profit is unchanged at 2pc, the Social Democrats are also stagnant at 2pc, Independents4Change are at 1pc, as are the Independent Alliance and Aontú.
The poll results came after Ms McDonald was robustly interviewed by Bryan Dobson on RTE television yesterday.
She was forced to defend her party's record in the North, including plans to increase the state pension age and massive hospital waiting lists.
And she admitted that the party's plan to raise €107m through a vacant site levy would see a large chunk of that windfall collected from local authorities.
She could not explain who would pay the €12bn subvention Northern Ireland receives from Westminster in the event of a united Ireland.
However, she said the British would "not walk off the pitch scot free".
Ms McDonald also said a Border poll was not a "red line" issue for her in government formation talks, although she added that the next administration should prepare for a referendum.
The interview came shortly after RTE did a U-turn and invited Ms McDonald to take part in a televised election debate along with Mr Varadkar and Mr Martin tonight.
The move followed a surge in support for Sinn Fein in recent polls.
However, Ms McDonald was under pressure last night over her grasp of her own election pledges.
She was asked to explain how her plans to increase the vacant site levy from 7pc to 15pc would raise €107m when last year it only raised €882,000.
Ms McDonald responded: "I'm not the costing unit of the department concerned."
She said she was aware most of the vacant sites being charged the levy are owned by local authorities and an increased charge could affect council services.
Under questioning, she also accepted the purpose of the levy was to release land, meaning that if it works, less revenue would be raised.
She also admitted that her party was given a free vote on increasing the state pension age to 66 in the North and decided to support the move due to concerns it would have on budgets.
She said keeping the pension age at 65 in the Republic, as they are promising, would have "blown a hole of £70m" in the Northern Assembly's budget.