A political three-card trick
It is the political equivalent of a three-card trick - a promise to cut taxes and cut the deficit whilst not cutting frontline public services.
There's no doubt that each of the cards the Conservatives played today is electorally popular.
The question is whether Labour and the Lib Dems can convince voters that, taken together, the promises are indeed a trick because they are to be paid for by a promise to simply cut unspecified government waste.
"The government 'efficiency drive' is one of the oldest tricks in the book. The trouble is, it's nearly always just that - a trick".
Those are not my words but those of David Cameron who used the argument to defeat those in his party who pressed him to pledge what he always described as unfunded tax cuts.
His shadow chancellor insists that given that two renowned government waste-busters have signed off their plan this promise of a tax cut cannot be described that way.
Whoever you believe, there's no doubt that today's announcement is very different from the talk of an "age of austerity" and the pledges of pain to come at the last Conservative Party conference.
Perhaps that should come as no great surprise. Since then the Conservatives have slipped in the polls and two-thirds of voters told one poll that they believed that the national debt could be paid off by the government if, you guessed it, they spent money more efficiently.