Something has happened to the Prime Minister. He has always been a cheerful optimist, but recently his Zebedee bounciness has been more marked. I understand the explanation is this: quite suddenly, he has seen how he might win the next election without the Liberal Democrats.
To appreciate the change that has come over him, we have to understand a Westminster paradox. The Conservative leadership thinks that it lost the general election last year. Everyone else thinks that David Cameron won, because he ended up as Prime Minister. But Cameron thinks he fell short. He hoped and expected to do better. It is hard for those on the outside to appreciate the blow to Cameron's confidence of the election result. Until now, I am told, he believed that it would not be possible for the Conservatives to win again on their own, and that he saw his best hope of retaining office being for the coalition to continue after 2015.
The proximate cause of the change in his outlook is that he has survived the crisis of the NHS reforms. Indeed, I am told that he thinks that the NHS pause was a "brilliantly executed operation". Splutter ye not: you can see how merely surviving with most of the planned changes intact is a Conservative gain. Although Andrew Lansley, the Health Secretary, shouldn't have got into so deep a hole, the Tories have now got out of it. They still haven't won over the British Medical Association, the doctors' trade union, but the BMA is a peculiarly reactionary force and most of the other interest groups in the health service have come round.
However much Nick Clegg tried to use the NHS to differentiate his party from the Conservatives, the end result is that the Liberal Democrats now support the reforms. Not just Clegg, whose creditworthiness with the voters has gone Greek, but Shirley Williams, who wrote in The Independent last month that the party had saved the "essential elements" of the NHS, and Paddy Ashdown, who hailed reforms to the reforms as a "victory for common sense".
On the fundamentals, therefore, Cameron thinks he is "in the right place". There is no alternative reform programme for the health service. Academy schools are gaining momentum. And the plan to cut the deficit is on course. My sources say that senior civil servants are even talking about what they might do if they achieve their 20 per cent cuts in central government staff numbers ahead of schedule.
Against this background, Cameron's belief, I am told, is that "U-turns don't matter". As long as he does not make too many of them, he thinks that the important thing is to do them quickly – "no one cares about forests now". Despite opinion poll figures suggesting that he is down six points on "Sticks to what he believes in", his view is that "no one thinks this isn't a strong government".
Cameron's change of mood also explains his apparently casual assertion of the difference between the "tougher" Conservatives and their Lib Dem partners in a Radio 2 interview two weeks ago. "If I was running a Conservative-only government, we would be making further steps on things like immigration control," he said, "or making sure that if you are not prepared to work, you can't go on welfare."
Thus Cameron gains the benefit of the Lib Dems' endorsement on "tender" policies, such as the NHS, while asserting the Tory claim to "tough" policies on immigration and welfare, which are also popular.
This works for him because a hung parliament takes some getting used to. We journalists keep forgetting that the Government is a coalition. I suspect the voters do too. Ed Miliband's attempt to brand it a Tory-led government may have backfired, because many people see it as a Tory government, but of a rather different character from Thatcher's.
To go back to the 2010 election, there are two reasons why the Conservatives did not win more votes. The first is that, despite all Cameron's efforts to promote "liberal, compassionate Conservatism" they were still seen too much as the uncaring party; the second is that, at a time of economic crisis, many voters looked to Labour to protect their jobs.
Both factors will have changed by the next election. The Lib Dem endorsement and the experience of government will help to persuade more voters that the Tories are not crazed and heartless. By 2015, when the blood-curdling rhetoric of the trades union and Labour leadership has been contradicted by Cameron's appearance as a humane and competent balancer of the books, the fundamentals will indeed have shifted in his favour. And, provided that the threat of a further economic crisis has receded, Labour's claim to offer job security will lose its power.
There are reasons for doubting Cameron's optimism. The NHS reforms have hardly started yet, and some of the few who actually understand them think that it will cost billions extra to stop the NHS becoming a vote-loser by the election. And who can say what will happen to the deficit-reduction plans when the cuts, still largely theoretical, meet the reality-based community? But you can understand why Cameron might feel that he can see his way through to winning a majority in 2015, and why he talks about Thatcher's 43-seat majority in 1979 as the sort of thing at which to aim.
One other thing that may help him is the converse of the Westminster paradox. Just as many Tories secretly believe that they lost the election last year, many Labour people secretly think that they won. Although Ed Miliband often says that Labour "lost, and lost badly", for many of his followers, these are just words. They think that they did not lose the election nearly as badly as they feared, and therefore won a sort of moral victory. All they need is a more personable version of Gordon Brown and a "Tory cuts" story.
No wonder David Cameron has rediscovered his inner Zebedee.