“The Spanish are very left wing…”
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Yes, most of their government are Democratic Socialists with a fair amount of card carrying communists among them.
The USA has communists in our government too, we changed their name to the Congressional Progressive Caucus though.
That is the current governing coalition. Governments have alternated right-left since Franco.
But none of that has anything to do with this. This is a peculiarity of the Spanish judicial system. Something like the “Hawaiian Judge” problem in the US.