BBC political editor Andrew Marr told the Six O'Clock news that the accusations against the Conservative leader could make or break him.
Mr Duncan Smith's leadership could be boosted
Iain Duncan Smith knows that it is really double or quits for
If at the end of this investigation Iain Duncan Smith is found to have broken the parliamentary rules that is the end for him really. It is finito as Tory leader.
On the other hand if he is cleared, it is probably good news for him.
A lot of Tories - whatever view they take of his leadership - feel that this is pretty underhand, the accusations are pretty dirty and if he is cleared there will be a great backlash of support for him.
One person said to me they thought these allegations had been put out initially to knock him off his perch, but that if he was cleared by this process he would be firmly nailed to it for quite a long time to come.
Over the weekend there have been enormous numbers of conversations between Tory MPs and their local officials about what to do.
My impression is that during Saturday and Sunday the mood to try and depose Iain Duncan Smith had cooled down a bit and the plotters were slightly on the back foot.
There have been further meetings
and that still seems to be the case.
But it may very well be that if Iain Duncan Smith is cleared of this,
that gives him the necessary three weeks, four weeks, five weeks
that he is hoping for to put all this behind him.
The plotters say they are still moving forward and they say they are still likely to move before Christmas.
Everybody is now going to be watching
the parliamentary watchdog
to see how he responds to this.
The future of the Conservative leadership is effectively now in his hands.