In theoretical terms, what this clarifies is the parameters of the Coalition Agreement. While almost every policy that Cameron highlights in his speech is part of that document, it seems that the Lib Dems don't have to agree with the way he sells them. The point is being made, this morning, that the idea of reducing net migration to its 1980s levels is very much, and very specifically, a Tory ambition.
But it's the politics of the situation that are considerably more intriguing. We know that we have entered a "new phase" of the coalition, where both sides more readily define themselves against each other — and understandably so. But this is still surprisingly acidic stuff from Cable. The question now is whether he might be overstepping the mark, or whether it's a sign of real breakdown in intra-coalition relations.
In any case, Cable's intervention is hardly going to endear him to those Tories who thought he should be forcefully retired after his unwitting Murdoch gaffe. It may be spring, but the bloom appears to be fading from the Rose Garden.