The Caerphilly Senedd by-election win for Plaid Cymru indicates dissatisfaction that extends beyond the town's boundaries.
Polling suggests Labour's collapse will be repeated on a wider scale in the Senedd elections and the next general election in Westminster.
This reflects a political trajectory evident across the industrial world, a backlash against the 'middle managers' of capital.
This is part of a general crisis among the UK's 'establishment parties', but also a global phenomenon.
Author's summary: Plaid Cymru's win indicates a broader dissatisfaction.