From where are the nominees for the President of the European Commission sourced?
This answer says:
"The European Parliament (the parties elected by EU citizens directly) nominates candidates. While not strictly codified in European law, it is common practice that each party group of the parliament nominates one person (this process is just described with the sentence "Taking into account the elections to the European Parliament and after having held the appropriate consultations" in 17.7. The practice of party group appointment grew historically)."
But where do the party groups look for their nominees? Their own members? Their friends? Elected officials somewhere?