At least one month before the election, the cantonal parties (in this case, the Social Democrats) must put forward their candidates to the national party.
A few days later the party leaders interview the candidates and make an initial recommendation to their own parliamentary group.
Approximately a week later the parliamentary group interviews the candidates again and draws up a shortlist. These names are then proposed to parliament (the Senate and the House of Representatives).
The shortlisted candidates are usually interviewed at a hearing by the parliamentary political groups.
One of the shortlisted candidates does not necessarily have to be chosen. It is a free vote for members of parliament. In theory, every person entitled to vote in Switzerland can be elected.