Some interesting new research on partisan identity: https://ukandeu.ac.uk/voters-brexit-and-the-limits-of-party-loyalty/
Voters who identified strongly with the Conservatives before
the referendum, for example, followed the party in becoming more Eurosceptic as
the party tacked in that direction. And voters who joined the Conservative
Party just after the referendum brought their other views in line with the
positions of the party: they soon became more hostile to economic
redistribution, for example.
Partisan identities still matter, even in countries, like
the United Kingdom, marked by increased electoral volatility and the ongoing
decline of traditional political loyalties.
All of this suggests that voters are still influenced by
major policy debates. On high salience issues, party loyalty has real limits.
Voters seem to care about at least some policies.