What's interesting about the situation of the Democratic Party in the US is that leftists like Mamdani are winning nominations within the party, then going on to win elections, but the centrist 'Corporate Dems' still won't support them.
Throughout the world, the centre-left's rationale for not allying with the further-left is that they will lose more centrist voters, and therefore lose elections.
Does the US example show... what ?
That they simply miscalculate - and in fact a bold left programme can attract more formerly disillusioned voters on the left than it loses in the centre ?
Or that the electoral rationale was always just a shallow rationalisation, and the centre-left just ideologically rejects the further-left - but disguises this ideology behind an imagined real-politik 'pragmatism' ?