Pressure is mounting on Fianna Fáil to declare whether it will support the government, in a motion of no confidence this week.

Fianna Fáil's government deal forces it NOT to support the motion - just as a new opinion poll gives it major leads over Fine Gael.

The government has already splitered over the Maurice McCabe affair, with three ministers telling Today FM they're deeply unhappy that Katherine Zappone withheld information about Tusla's role in the scandal, during last week's cabinet meeting.

Now that unhappy partnership faces a twofold threat from outside.

Sinn Féin is to use its Dail time on Wednesday to table a motion of no confidence in the Fine Gael-Independent government.

Fianna Fail's confidnce and supply arrangement obliges it either to vote against, or abstain on, that motion.

That, at a time when a new Sunday Times poll out this morning shows Fianna Fail with an 11-point lead over Fine Gael.

And knowing Enda Kenny is refusing to relinquish the reins in Fine Gael, but also not prepared to lead another election campaign, the prospect of major electoral gains will be tough to resist for Fianna Fáil.

New Politics will never face a bigger test than this one.