When a fresh-faced Tony Blair vowed to "turn round" the issue of law and order after he became shadow Home Secretary in 1992, some Labour colleagues thought he would never neutralise one of the Conservative Party's most powerful political weapons.
It was one of the rules of the game that the Tories were tough on crime, and Labour soft.
The public liked the tough stuff and so would always trust the Tories more on the issue. Yet Mr Blair confounded the sceptics and showed that long-held perceptions can be changed. An impediment to a Labour election victory was removed.
Now the Tories are trying the same trick on the National Health Service. The public knew it was Labour's baby and, although Tory governments pumped in billions, felt that the Tories never really believed in it.
This week, the Opposition went on the front foot as they launched a campaign that set out their initial policy ideas and harried the Government over the financial problems in the NHS. Mr Cameron drew blood at PMQs, when a strangely under par Tony Blair struggled to explain the current problems and played into the Tory leader's hands by admitting there were "cuts".
Why is the see-saw moving? In classic Blair style, Mr Cameron has eliminated his party's negatives. He has dumped the ill-fated patients' passport, under which a Tory Government would have met half the cost when people opt for private treatment. He has promised that NHS treatment will be free and tax-funded, and to "never" bow to pressure from the Tory right to bring in social insurance.
So Mr Cameron has shot many of Labour's foxes. Ministers can hardly accuse the Tories of privatising the NHS when the Government itself sets no upper limit on the private sector's role in carrying out state-funded treatment. Ministers were privately fretting the Tories would set such a ceiling, putting them to the left of Labour on health. They were mightily relieved the Tories did not announce one.
Another factor working in the Tories' favour is that Labour's medicine doesn't seem to be working. There is a daily dose of bad NHS headlines even though Labour has doubled spending - which a majority of people think has been wasted. That creates an opening for the Tories. "If money were the problem, it would have gone away," said Stephen Dorrell, the former Health Secretary, who chairs a group drawing up Tory policy on public services.
Mr Cameron also brings something to the party. Having a disabled son means he relies on the NHS, a useful antidote to Labour charges that he is an Eton-educated toff. His message seems to have cut through. According to Populus, 50 per cent of people think the Tory leader believes in the principles of the NHS and wants to improve it for everyone --a higher rating than Gordon Brown (45 per cent) or Mr Blair (42 per cent).
Other surveys suggest the Tories are more trusted than Labour on the NHS and have the best policies. That is quite a turnaround, although I suspect it reflects disenchantment with the Government rather than positive endorsement of a still hazy Tory policy. The Tories will need to work hard to overcome their credibility problem.
But Labour MPs are jittery. The national press headlines are magnified at local level, as hospitals are slimmed down to bring care closer to people's homes. Backbenchers wonder why Labour is on the defensive on home ground. Patricia Hewitt, the Health Secretary, who has been summoned by shop stewards representing Labour MPs, will defend her strategy in a blitz of activity next week.
Yesterday, Labour fought back by issuing a dossier accusing the Tories of running a "dishonest and misleading" campaign and contrasting Mr Cameron's "new-found faith" in the NHS with his track record. Labour pointed out that Tory claims about 20,000 NHS job cuts are wide of the mark. Cutting posts or not filling them is not the same as sacking staff.
In fact, both main parties wrongly cry "cuts" to frighten the voters. Labour claims the Tories would cut the budget by £3bn but Mr Cameron is likely to match Labour's spending. His refusal to offer tax cuts may help him reassure the public.
Labour is paying the price of being in power for almost 10 years and is getting little credit for an improved service. Niall Dickson, chief executive of the Kings Fund think-tank, said Labour had made a "significant achievement" by reducing waiting times, which would not have been achieved without the Government's much-derided targets. Although the Tories would scrap them, they need some incentives to make the system work.
He warned the Tories to beware handing power to "vested interests" under their plan to transfer day-to-day running of the NHS from the politicians to the professionals.
He believed the Tory proposal for an independent NHS Board, also floated by Mr Brown, would not necessarily cure all ills. "It would be a mistake to believe it would ever be possible to remove politics from a life and death service that consumes £100bn of public money every year," he said.
Mr Dickson said the Tories were "riding a populist wave" against changes at local level that they would have to implement if they were in power. "There are no fundamental differences between the two parties," he said.
The Tories are unlikely to win the NHS war. But they might just snatch a draw. If they do, the rules of the game will change again.