In a "First past the post" electoral system, It's always more advantageous for the 3rd party to merge with the first or second party. New Zealand changed away

In a "First past the post" electoral system, It's always more advantageous for the 3rd party to merge with the first or second party. New Zealand changed away from First Past the Post to Mixed Member Proportional in order to fix that https://en.wikipedia.org/wiki/Mixed-member_proportional_representation https://en.wikipedia.org/wiki/Mixed-member_proportional_repr... https://en.wikipedia.org/wiki/Electoral_system_of_New_Zealand#MMP_in_New_Zealand https://en.wikipedia.org/wiki/Electoral_system_of_New_Zealan... I'm not sure how you'd implement it, particularly at the senate level.