IT has been a seismic week in the economic history of this Republic. The tectonic plates beneath us have been shoved around by forces that are no longer under our control.

It has been a seismic seven days in the history of Fianna Fáil too. The very future of the Soldiers of Destiny has been questioned – and a fair bit of that questioning has come from inside its own parliamentary party. Taoiseach Brian Cowen has had his worst week as leader of the country, so much so that it is now a matter of when, rather than if, his leadership will be challenged.

At midnight last Wednesday, Cowen avoided the unwanted distinction of going down in history as the shortest-serving taoiseach, surpassing John Bruton's tenure in office. But avoiding that particular wooden spoon was a pyrrhic victory for Cowen in a disastrous week.

The Fianna Fáil organisation has been left shell-shocked and demoralised, and the finger of blame is being pointed firmly at Cowen, with a large number of TDs stating that he is "beyond repair in the eyes of the public". One member of the parliamentary party remarked wryly: "It will be interesting when Cowen's popularity goes below the value of the yield on Irish government bonds."

Morale in the party is at levels probably never seen before in its 84-year history. For now at least, a lot of the fight seems to have gone out of Fianna Fáil TDs. Even Pat Rabbitte's outburst against Minister Pat Carey on Thursday night's Prime Time did not prompt the usual Fianna Fáil circling of wagons.

"He may have been grandstanding a bit. I don't think he meant to do it but he lost the rag. But there was very little that Pat Rabbitte said that I could disagree with. We are diminished," said one senior party figure.

Rabbitte's line about the Republican party overseeing the intervention of the EU/IMF particularly hit home.

"I'm not on the green wing of the party but when I saw [British chancellor] George Osborne on the TV talking about how Britain would be prepared to help, my blood went cold," one TD said.

There is huge anger among deputies at Cowen's handling of the imminent arrival of the IMF delegation. And there is precious little sympathy for the not unreasonable defence that the government believed any admission that an EU/IMF bailout was imminent would strongly weaken its negotiating hand before the talks began. The public perception, they say, was of a leader who failed to communicate what was happening to the country in a week of national crisis.

"We were spoofing and you can't spoof about this," the senior party figure said. "Whatever good intentions were behind it, it contrived to suck whatever spirit was left in the place."

The atmosphere in the Dáil during the week was almost funereal, with one TD commenting, only half-jokingly, that "all you needed was some tumbleweed blowing down the corridor". Several deputies said the mood in the Fianna Fáil parliamentary party had turned "very fractious", with TDs "snapping at each other".

And the atmosphere back in their constituencies is even worse. One TD reported that he had been "chewed out of it" on the street on Friday. More worryingly for the party, another TD said people had stopped complaining and were simply walking past him.

The belief in the parliamentary party is that if a general election was held in the next few weeks, a return of "30 to 35 seats would be a good result and there is every possibility that we'd go below 30". Senior sources say that "an awful lot of people, running into double figures, are considering not running again. It's so raw at the moment."

While emotions will inevitably cool over the coming days and weeks, talk has turned, yet again, to Cowen's leadership. Backbenchers and more senior figures – not from the dissident wing – told the Sunday Tribune this weekend that Cowen could not lead the party into a general election in spring and a challenge to his leadership was inevitable. They stressed that nothing will happen before Christmas because of the need, in the national interest, to pass the budget and get approval for the four-year plan. But after Christmas, they say, there will be a move against the Taoiseach.

"There will be [a heave] and it will succeed," one influential TD said. "You know what I think of him [the Taoiseach]. I am a big fan and I think he's got an awful hard rap but I'd have to think of [backing] it myself."

This was echoed by another well-respected backbencher: "I am somebody who would always back the leader but he cannot lead us into the election. It now looks like we will be facing into a general election in the spring. Cowen is a leader who will not want to leave office himself so I would expect that there will be a move against him straight after Christmas."

There are serious doubts that any of the cabinet will publicly back a heave against Cowen but several backbench TDs say there are enough of them to move a motion of confidence against the leader. One well-regarded backbencher is understood to have made it known that he will be willing to act as a stalking horse if required; others said this weekend they would have "no compunction in telling Cowen it's time to move on".

The usual names are being mentioned as successors to Cowen – Micheál Martin, Brian Lenihan, Dermot Ahern and Mary Hanafin.

"It is hard to know who will replace him as a lot of people have been contaminated by the past," one senator said.

A number of deputies said "Lenihan's star is on the wane" and identified Hanafin as the minister who was emerging as a real contender. "She was brilliant last week," one minister remarked.

Cowen's best protection is that the general election is so close and there must be serious doubts as to whether a new Fianna Fáil leader could be elected taoiseach, even on an interim basis. TDs accept that, whoever is leader, large seat losses are inevitable but a sizeable group seem determined they will not "sleepwalk" into the next election with "Cowen's face" on the election posters.

Their mood was summed up by one Dublin TD who said: "Our only hope of survival is to go before the electorate with a new leader".