By Nick Assinder
Political correspondent, BBC News website
David Cameron set himself a big enough challenge when he attempted to persuade voters his top priority was the health service - often seen as Labour's greatest single creation.
Mr Cameron has pledged to put the NHS at the top of his agenda
Now he is pushing further, as the service celebrates its 60th anniversary, he says his aim is nothing less than to see the Tories replacing Labour as "the party of the NHS".
Not too long ago such a statement would have brought gales of laughter from Labour MPs (and not a few opposition ones).
They would have pointed to the Conservative Party's previous record on the service which, rightly or wrongly, they would insist was marked by either outright opposition or attempts at privatisation.
The old cry was that the NHS was not safe in Tory hands. It was a cry deployed by Tony Blair with some power before the 1997 election when he claimed there was just 24 hours to save the service.
So, perhaps David Cameron's best option might be to stick to safe Tory territory such as law and order.
Except, of course, the great political convergence of the past decade has pretty much ended those old certainties.
And one of Tony Blair's greatest achievements before that 1997 landslide was to finally kill off the notion that only the Conservatives could be more trusted on law and order and the economy than Labour.
Far more important is to convince voters the old, ideological divide between Labour and the Tories has gone
His success in re-branding New Labour as the party which was "tough on crime" was a turning point in its fortunes.
Mr Cameron wants to pull off the same trick on the NHS. Nail that one and a huge, historic electoral weight will be lifted from his party's shoulders.
And it is not simply because Mr Cameron can point to hospital acquired infections, dissatisfaction amongst staff and claims the service has been broken up by devolution.
Or even a perception - robustly challenged by the government - that, despite all the extra cash, the service has got no better over the past ten years.
Far more important is to convince voters the old, ideological divide between Labour and the Tories has gone.
Mr Cameron needs to show it is no longer a simple case that Labour will retain a nationwide service financed entirely by taxation and free for all at the point of use while the Tories would look to push market solutions into a two-tier service with the wealthy opting out in favour of private health.
And it seems he has already taken great strides in that direction, partly because of a change in policy away from ideas like patients' passports - seen as a boost to private health and undermining the NHS.
And partly because of big speeches, like the 2006 conference performance when he echoed Tony Blair's "education, education, education" pledge with his own "N-H-S" promise.
But, perhaps more significantly, his task has been made easier because the government has already introduced the market into the service.
Competence and trust
As Tony Blair regularly claimed, patients are far less bothered about how their care is provided or financed, so long as they get the best care available.
Ironically, the more Labour won that argument, the harder it became for ministers to attack Tory "privatisations" and the easier it became for the opposition to cast off its old image.
As a result, as in so many other areas, the argument now boils down to one of competence and trust.
There will be policy differences, but more often than not they will be on the detail - as Mr Cameron's pledge on tackling hospital infections has shown.
The NHS does not at the moment appear to be an ideological battleground.
And for Labour, that makes it far more difficult to claim the NHS as only their issue.