After all, when Cameron promised Guardian readers a "massive, sweeping, radical redistribution of power" he failed to identify what it might mean, except that he would seriously consider fixed term Parliaments. Today, he plucks a contradictory proposal out of the air: that any Prime Minister who takes office mid-term should call an election in six months.
It is very easy to predict that, were Cameron elected, neither proposal would resurface to trouble the statute book before 2015.
As Kettle outlines, Cameron wants to imply the Brown premiership is somehow unconstitutional - sweeping through those of John Major, Jim Callaghan, Harold Macmillan and Alec Douglas-Home in our Parliamentary democracy too.
Yet one Prime Minister did adopt Cameron's proposal: Anthony Eden, who won a thumping victory just a month into his disastrous year and a half premiership. Insisting on an immediate post-Suez election might well simply have forced an entirely broken PM to be propped up in office.
But let's do the man who wants to be Prime Minister in a fortnight the courtesy of taking his proposal seriously for a moment.
It would have, in practice, a paradoxical effect.
Not more elections under new Prime Ministers - but, rather, it would insulate unpopular Prime Ministers and make them much more secure until the eve of an election, because the nuclear threat of a quick election would be a reality.
Cameron's proposal would have cost the Conservatives the 1992 election: not, as it implies, because John Major would have had to go in the Spring of 1991, but because it would have prevented the party changing its leader at all.
I doubt Cameron is being sneakier than we think - but any incumbent PM would be a significant beneficiary of his proposal. So might he have had in mind not the past, but the future, not Gordon Brown, but Boris Johnson!
If David Cameron does wobble across the finishing line, with the Tory press gnarling, the 'sceptics champing at the bit, the economy in trouble, and the ever so helpful Boris lurking across the river, might there somewhere in the subconscious mind lurks the thought that he could use an insurance policy to make himself coup proof if it all goes wrong?
Though depriving the Tory party of its much cherished potential to wield the knife on its own leader when in power could be harder than it looks!
PS: There is a more coherent idea lurking underneath the surface. Cameron appears to believe, in effect, in directly electing Prime Ministers. And anybody who was seriously committed to the majoritarian principle of democratic elections - that full governing power should go to the leader or party with more votes than any other - surely ought to be moving away from the Russian roulette that first-past-the-post has become.
Advocating a directly elected Prime Minister, instead of crossing your fingers over the electoral geography, could be the only coherent way to make majoritarianism work.
If he thought about it, David Cameron might think that. But he probably hasn't.
Hopi Sen has been through the post-war card - and suggests Cameron's proposal could have seen Thatcher lose in 1976.
Cameron gets a bit snippy when The Observer suggests that proposing a major reform in mid-campaign is panicky, but he has a priceless defence of the problem of a 1940 snap election:
There were changes of prime minister during both world wars: from Asquith to Lloyd George, and from Chamberlain to Churchill. Under his proposal, there would have been snap elections in the middle of these conflicts. The forehead furrows, then he rallies: "This is a proposal for the future, not the past." He adds that "in the modern world people feel rather cheated" if they haven't voted for the prime minister.