The latest poll ahead of next weekend's General Election in the Republic of Ireland has put Sinn Fein tied with Fianna Fail.
A Red C poll published in Sunday's Irish Business Post recorded a surge in support for Sinn Fein heading into the final week of campaigning - with the party level with Fianna Fail, having overtaken Fine Gael for the first time.
Fine Gael and Fianna Fail are preparing a ground war to halt the onward march of Sinn Fein.
The latest poll has Fianna Fail on 24% (down 2 points) as is Sinn Fein (+5), with Fine Gael on 21% (-2). Among the other parties, Labour is on 5% (+1), the Greens are on 7% (-1), and Independents on 12% (-2).
With less than a week to polling day, Fianna Fail leader Micheal Martin has told Independent.ie that he would not rule out entering into a confidence and supply arrangement with Fine Gael if Leo Varadkar's party was in opposition as the smaller of the two parties.
As Fianna Fail and Fine Gael continued to clash on tax promises and each insisted there would be no role for Sinn Fein in the next cabinet, Mr Martin said he was confident he would be able to form the next government without Fine Gael's input. But when asked about the possibility of a confidence and supply arrangement underpinned by Fine Gael, he said: "I haven't ruled that out."
So great is the concern at the rise in Sinn Fein support that pressure will grow in Fianna Fail to consider asking traditional Fine Gael voters to 'lend' them their support to keep Mary Lou McDonald's party out of office - a reversal of the move made by Fine Gael's Phil Hogan before the 2011 general election.
Former Fine Gael leader Alan Dukes said an alliance between the two largest parties, including a possible grand coalition, could be the "only viable option" after the election if they continue to rule out Sinn Fein, whose support Fine Gael and Fianna Fail are privately acknowledging is rising across the country. "You could conceive of a situation where that would be the only viable option but whether it would apply or not I don't know," Mr Dukes said. "I think it's conceivable."
Two senior Fine Gael cabinet ministers told Independent.ie they would be open to the idea of a confidence and supply or grand coalition arrangement.
But the Fianna Fail leader has firmly ruled out a grand coalition and the party's deputy leader Dara Calleary yesterday also said: "There's no logic to that outcome. People want Fine Gael out of office. We would be ignoring that need for change."
Mr Martin also said he did not see a repeat of the confidence and supply deal that saw Fianna Fail facilitate the minority Fine Gael government "arising".
But he said other parties "have to play their part after the next election".
As well as not ruling out a confidence and supply deal, when asked how he felt about a rotating Taoiseach, the Fianna Fail leader said: "I don't think it is a sustainable option at this stage."
In his interview with Independent.ie, Mr Martin also launched his most strident attack on Fine Gael to date, saying: "They come from a more privileged background and they never really had that feel for working-class people."
Mr Martin said his own working-class background and opportunities through free education "sums up Fianna Fail". "The working-class person who wants to aspire and get on in life. To create opportunities - no matter what your background. I don't think Fine Gael come from that milieu," he said.
He added Fine Gael has a "huge sense of entitlement", a sense of "privilege" and believe "they have a divine right to rule".
"It is more instinctively a party who always looks after the wealthier classes and always has since its very foundation. It has a sense of privilege."
Meanwhile, a senior Sinn Fein source said the party would be open to talks with all parties after the election but signalled the party's preference to work with Fianna Fail.
"People want change," the source said. "They want Fine Gael out, it's nine years they're there and do they want Fianna Fail in there on their own?"
On the campaign trail yesterday, Sinn Fein leader Mary Lou McDonald dismissed as "stupid, silly and childish" the row between Fine Gael and Fianna Fail over which of them would ultimately do a deal with her party. Her party yesterday published legislation to reduce the age of retirement to 65 which Ms McDonald said it would introduce in the first 100 days in government.
Taoiseach Leo Varadkar, speaking as he canvassed in Cork, insisted everything remains to fight for in the final week of the campaign - and warned that senior Fianna Fail officials believe they already have "this election in the bag" and are preparing for ministerial offices, advisers and Garda cars.
Mr Varadkar insisted that a Fianna Fail-Sinn Fein coalition would be an economic disaster. "Is it change for good, which is what Fine Gael has been delivering, or is it change for the worse which is what Fianna Fail and Sinn Fein would deliver?"
Mr Varadkar insisted that Fine Gael can bounce back in the final days of the election campaign - despite the indications of numerous polls - when people realise what is at stake for Ireland given the challenges of Brexit and global trade.
He also claimed that some within Fianna Fail are behaving as if the February 8 General Election is already won. "I think there are elements in Fianna Fail who think this election is in the bag for them," he said.
"They are probably measuring up [Dail ministerial office] curtains, appointing advisers and talking about bringing back Garda cars.
"That is the kind of arrogance we are seeing from Fianna Fail - I hope they get a surprise next weekend."
One of the TDs who Mr Varadkar name-checked as supporting a Fianna Fail coalition with Sinn Fein last night said the Taoiseach was wrong.
"That's a definite no from me," Waterford TD Mary Butler said. "My position has always been the same."
Fianna Fail deputy leader Dara Calleary claimed that a vote for Sinn Fein was a vote for a vote to return Fine Gael to power. "People want change and that's what you get. You can vote Sinn Fein and get Leo.
"Mary Lou will do a deal with Fine Gael. I'm not convinced that Leo won't do a deal with Sinn Fein. He hasn't proven that he wouldn't whereas we have with Micheal in 2016," Mr Calleary said.