The EU is a new form of political organisation which can be defined as an “experimental polity”. Its distinctiveness lies in a novel assemblage of the constituent elements of polity (boundaries, binding authority, and bonding ties), and in the constant testing of new combinations of such elelements when facing functional and political challenges. Experimentalism is not always successful and can occasionally trigger off dynamics of polity disruption. The paper illustrates two instances of ‘bad experiments’ along the bounding and binding dimensions, i.e. Brexit and the euro crisis. It then focuses on the Covid 19 crisis and shows that in this case EU leaders were able not only to launch an ambitious plan of response based on joint action, but also to re-establish an “ethos of togetherness” among the Member States, on which to build for securing both social solidarity and political stability.