By Nick Assinder
Political correspondent, BBC News website
When you are on a roll, the trick is to keep the momentum running in your favour.
Gordon Brown had it before the summer holidays, and lost it after his bungled general election stunt.
Mr Cameron is talking about population growth
David Cameron had lost it but, thanks to Mr Brown, has found it swinging dramatically back in his direction. His task now is to keep it going his way.
To that end, he has made a couple of eye-catching announcements aimed at keeping the spotlight firmly on the Tories, and Mr Brown on the back foot.
In the past couple of days that has seen him tackling the hugely-sensitive issue of immigration and suggesting a ban on Scottish MPs voting on England-only legislation.
In his first major speech on immigration and population growth, Mr Cameron has called for a "grown up conversation" on the issue which is seen as of increasing concern to voters.
By that he clearly means he does not want to be portrayed simply as "lurching to the right" in an attempt to keep his right-wingers happy with anti-immigration talk.
He had enough of that during his party conference earlier this month during which he appeared to focus on the sort of issues like tax and Europe that appeal directly to that wing of the party which had been showing signs of cutting up rough.
Now, he has latched on to the recent report suggesting the UK's population is set to increase by 4.4 million to 65 million by 2016 with the figure hitting 71 million by 2031.
Mr Cameron wants a grown up conversation
There are several reasons for that - higher life expectancy and birth rates, for example - but net immigration is the major factor, accounting for some 70%.
At the same time there is a growth in people living alone, what Mr Cameron calls the "atomisation of society", increasing the number of households.
So the Tory leader is framing his arguments in terms of population growth and demographic change rather than purely immigration, taking some of the emotion out of the issue, he hopes.
None the less, it still boils down to reducing the level of net immigration into Britain from non-EU states (it is not possible to curb migration within the EU).
Mr Cameron has repeated his pledges to create a separate border police force, introduce transitional immigration controls for new EU entrants, change the rules on spouses entering the UK and ensuring UK workers have the skills to fill job shortages.
Whether he will escape claims he is simply back on the old Tory agenda on immigration remains to be seen, however.
Meanwhile, the move on English-only legislation allows the Tories to claim they are the only party with any new ideas on the famous West Lothian question which, they believe, is of growing concern both inside and outside Westminster, thanks to devolution and the rise to power of the SNP.
But - and this is not simply a happy coincidence - it also serves to once again highlight the prime minister's Scottishness.
For example, if the Tory policy is implemented, it could see the prime minister introducing legislation he is then banned from voting on.
Mr Cameron's aim with both these big issues is to keep hold of the agenda and suggest the government is lacking coherent, realistic polices in these areas.
The fact that both may also appeal to the right-wingers in his party he will undoubtedly claim is a happy coincidence.