In the Dutch political system, political parties don't have clear formal 'leaders'.

The Dutch political system is dualistic, with a split between members of parliament and members of the cabinet.

But informally, parties do have clear leaders.

Sometimes it's the leader of the party's parliamentary fraction, sometimes it's a cabinet minister or the prime minister.

The party chairperson is often an obscure administrative figure and not a leader in the sense of this question.

This question identifies a number of Dutch politicians as leaders of their party.

The question is who ceases to be leader of their party first?

This question resolves after either:

An announcement that they resign as leader or withdraw from politics or a transfer of the leadership to someone else, even if the leader stays on in a caretaker capacity until a successor is chosen.

The leader is dismissed by the party leadership.

The leader loses an internal party election.

The leader is permanently physically incapacitated.

The stated resolution date is arbitrary and will be extended if the question hasn't resolved by then.

Only the parties and leaders listed in this question count, we're not interested in minor parties.

If the leader changes in government position, it won't count so long as they remain party leader.

If a political party changes its name or organisation and the leader stays leader of the new party, it won't count, so long as the old party ceases to be relevant.

For Frans Timmermans, if GL-PvdA fuses together into a new party and he stays leader, it won't count.

If the parties split apart into separate GL and PvdA fractions, and he retains leadership in one of the fractions, it will count as ceasing to be leader.

In cases where a party institutes a co-leadership including one of these leaders, it won't count as losing the leadership so long as the listed leader has not permanently taken on a subordinate role.

For example, if Pieter Omtzigt has a prolonged leave of absence, it won't count if the absence is stated to be temporary.

In cases where it's ambiguous whether someone resigned as leader, I will make a judgment call.

Perhaps based on media consensus that they resigned.

Cases where a leader only metaphorically loses their leadership position don't count.

Cases such as when the media deems a party 'leaderless' or the leader has no real authority or their ideas are no longer followed.

If there's nobody else who issues a challenge and wins a leadership contest, they are the leader.