By Nick Assinder BBC News Online political correspondent

They believe, almost certainly correctly, that there will not be a move to oust him this week.

And, with the current state of the Tory party, a week without a leadership challenge, or the threat of one, is seen as a major success.

But the party bosses should also know that, like London buses, another one will be along in a minute.

What is abundantly clear from the latest bout of Tory in-fighting is that Mr Duncan Smith's desperate "unite or die" warning - issued the last time he was under threat - has been flatly ignored.

Admittedly, the Tory leader brought the latest crisis on himself with his re-shuffle in party headquarters.

His understandable suspicion over the plotting Portillistas appears to some to have clouded his judgement and he has fallen back on his right wing instincts.

Shot himself

Whether the personality changes at Central Office translate into policy changes still remains to be seen.

But Mr Duncan Smith must have known that the moves would provoke his more left-wing enemies within the party.

Portillo escalated crisis

Even his supporters were dismayed that, just as Tony Blair's leadership was under question like never before, Mr Duncan Smith picked up his service revolver - and appears to have shot himself in the foot.

The powerful 1922 committee of Tory backbenchers may now even ask their leader to explain to them precisely why he did that.

That is an explanation just about everybody in Westminster would like to hear.

Presumably he thought the personalities involved were so unknown that he could get away with it without a row.

That misjudged the readiness of his enemies to leap on every action to whip up discontent.

And, once Mr Duncan Smith had committed that apparent misjudgement, Mr Portillo leapt on it and made matters dramatically worse.

Eager to strike

It was almost entirely a result of his intervention that the feverish speculation about an imminent leadership challenge erupted.

There is little doubt that the Portillistas, or "mods", in the party are eager to strike.

And - thanks to Mr Duncan Smith's improving Commons performance and the chances of a good Tory showing in May's local elections - they may fear their chances of victory are about to fade.

If the party does do well in May it will become extremely difficult to remove Mr Duncan Smith. That is precisely what happened to his predecessor, William Hague after his election.

So it may be that the mods are keen to dump Mr Duncan Smith before May.

But that would be hugely damaging. Sacking a leader in war time is the height of bad taste and could easily backfire.

Do nothing

And there is still the same old problem of who exactly they think should replace Mr Duncan Smith.

That almost always ends up with speculation over a Ken Clarke campaign backed by Mr Portillo. Or a David Davis challenge.

And, thanks to the new rules which ensure ordinary party members get the last word, unless the MPs stitch up a succession without the need for an election, the outcome would still be dangerously unpredictable.

So, what should Mr Duncan Smith do to hang onto his position?

Probably the best advice is, nothing.

He should probably drop the hyena impressions, block out any sense of paranoia, refuse to play his enemies' game and simply get on with the job of harrying the government.

That will not stop the sniping or speculation over a leadership challenge. But at least it probably won't make matters any worse.