Eighteen months ago, someone at Channel 4 News  made a smart call. It was autumn 2008 and the programme's makers were keen to discover whether Gordon Brown's role in "saving" the banks would ultimately save his premiership. But rather than test the mood of the country as a whole, the show set about polling in marginal constituencies.
And not just any marginals. The seats where David Cameron's Conservatives only needed to overturn a lead of a few hundred were irrelevant -- Cameron had those in the bag long ago. Rather, YouGov was asked to look at seats where Labour had majorities of roughly 2,000 to 7,000 votes, the very seats the Tories have to win if they want an overall majority.
In other words, these are the marginals that matter.
This week, YouGov returned to those 60 Labour-Conservative constituencies and last night Channel 4 News broke the bad news  to Cameron and co -- the Tory lead over Labour is just 2 points, translating to a Conservative government 11 short of a majority. This is hung parliament territory.
The figures themselves are not disastrous for the Conservatives but the trend is worrying, suggesting a loss of that electoral magic formula: momentum.
Back in October 2008, despite the bailout bounce Brown was enjoying elsewhere, the Tories had a commanding 13 per cent  lead in these 60 seats. Moreover, Cameron's personal ratings comfortably trumped Brown's. Not any more. For example, 70 per cent now think that David Cameron in No 10 would mean either change for the worse or no change.
If Mr Cameron can't turn that round, and if the general election results are exactly in line with our poll, then the Tory leader would unquestionably become prime minister, but he may need to call an early second election to seek a clearer mandate from Britain's voters.
And if he continues to lose momentum in these seats, things could be even worse. As it says on this week's New Statesman cover: "Game on ".