Politically extinct 

A: When an individual or group ceases all political activity and never becomes politically active again
B: A situation where a particular political ideology or party has so little support that it is seldom mentioned or discussed in political interactions; regardless of whether those interactions are held in public or in private

An example of a political party that is politically extinct is the Whig Party. It began going extinct in the early 1850s while trying to recover from the presidency of Franklin Pierce. It was trying to form platform to run on in future elections, but they were unable to form an effective platform and over time they began losing large amounts of support to the point at which the party eventually collapsed.

Politically extinct by Vanguard 1998 July 2, 2021

Political extinction event 

An event that causes, or has the potential to cause, numerous people, organizations, political parties, and, in some cases, politically ideologies to become less common to the point where they are no longer are discussed and or are active in politics

The presidential election of 2020 was a political extinction event for certain political parties. Some parties that were affected may include Independent Party of Connecticut, American Delta Party, Reform Party of Florida, and Independence Party of New York.

Political extinction event by Vanguard 1998 July 3, 2021