By Nick Assinder
Political correspondent, BBC News website
If there is one gene politicians seem to lack in their DNA it is the one which controls the ability to stand firm in the face of hostile fire.
In difficult times they tend to behave like kittens facing cobras - they either become glued, transfixed and trembling to the spot, or they bolt in blind panic.
David Cameron has suffered recent setbacks
Occasionally they display a version of another piece of animal behaviour, and devour their own.
And, as MPs prepare themselves for the long summer break, both Tory leader David Cameron and the Liberal Democrat's Sir Menzies Campbell are nervously eyeing up their own troops for signs they are licking their lips.
What has surprised many in Westminster is just how easily Liberal Democrat and, much worse, Tory MPs appear to have been spooked by Gordon Brown's "bounce".
They all knew it would happen, because every new prime minister experiences it in the weeks and months after getting the job.
And they have had plenty of time - at a very minimum 12 months - to prepare for it.
Yet near-panic appears to have set into parts of the Tory ranks while the Lib Dems have also shown signs of severe jitteriness.
The Brown bounce has worried opposition parties
David Cameron has been forced to tell his party, for the umpteenth time, that he is not going to be blown off course in his drive to push the party back onto the centre ground.
Sir Menzies Campbell has issued a "hold your nerve" message to his troops.
But it is not simply Gordon Brown's success in seizing the momentum while closing off areas of advantage to the other parties, in an attempt to force them off the centre ground, that is responsible for much of this.
It is also because both those uneasy members of the opposition parties are those who have had doubts about their own leaders all along, doubts which been sharpened by recent events.
Mr Cameron's woes - by-election setbacks, the grammar schools row, criticisms for leaving the country during the floods and sniping by senior supporters - would still have happened without Mr Brown.
And the fact that many Lib Dems have serious misgivings over Sir Menzies' leadership have not emerged as a result of Mr Brown's succession.
So what can the two leaders do about it?
Firstly, and it is something Sir Menzies appears to have taken on board, get the "don't panic Mr Mainwaring" message across.
Sir Menzies has put party on election alert
History dictates that the Brown bounce will wear off - no prime minister has a limitless supply of new initiatives.
Mind you, for some, that fact has only added to the panic by suggesting the prime minister will, therefore, call an autumn election to take advantage of his current standing.
Even Sir Menzies seems to have fallen for that one, putting his troops on alert for an October poll and saying there is a "one in six" chance of it happening.
At least he has silenced much of the rumblings over his own position with two second-place by election performances which headed off the worst.
He is now looking towards a party conference in the autumn that, he hopes, will not be dominated by talk of his own position but which will concentrate on "good solid work" on policy.
Mr Cameron's task is to rise above the sniping from what is only a small group of dissidents and start putting some flesh on the bones of his policy programme.
That is due to happen this summer with the autumn conference scheduled to be the one where he starts moving on from the all-spin-no-substance criticisms.
Mr Brown's success in taking strategic decisions which have crowded the Tories out and limited Mr Cameron's room for offering fresh, distinctive policies means he is searching for something big to symbolise his party's transformation.
That process has started with, for example, former leader Iain Duncan Smith's widely-admired review of policy aimed at repairing the "broken society".
And there will be more to come. But the battle Mr Cameron is engaged in now is to show it is the Tories who offer the "change and newness" that voters are said to be searching for and which Mr Brown is determined to offer.
The temptation is always to try and appease the right-wing over issues like Europe, and he has already tried that one. But too much of that will play right into Mr Brown's hands.
A retreat to traditional policies would give the prime minister plenty more opportunities to declare, as he did this week, that Mr Cameron was "back to the old agenda".