The Syriza example points us particularly to two decisive features of law-sterity. Firstly, by posing the situation as essentially 'radical break' or 'progressive austerity', it operates as a wedge with which to split the radical and moderate components of any political coalition, generally leaving the latter in power. Secondly, whilst 'progressive austerity' may be implemented under protest, one cannot implement such a regime without being fundamentally transformed. Such a government will - necessarily - become alienated from its base and continue to make compromises, eventually internalising the very logic of austerity (particularly as the more radical elements in its ranks are driven away). I this way, there is a double movement towards transforming progressive governments into austere subjects.
he's using double movement in a different sense than Polanyi but this is good analysis