After being excluded from later Democratic debates, Mike Gravel ran for the Libertarian presidential nomination in 2008 but failed to win it.
Notes on verification
Confirmed by multiple independent sources including CBS News, Wikipedia, and Ballotpedia, all corroborating the sequence of events and outcome. [cascade flags: wikipedia_dropped_other_sources_exist | tier=silver indep_score=0.875 clusters=2 claim_tier=notable]
Sources
- Mike Gravel, former US senator for Alaska, dies at 91 (seed:politics_and_current_events)
- https://www.cbsnews.com/news/mike-gravel-dies-former-senator-alaska-presidential-candidate/ (corroboration)
- https://ballotpedia.org/Mike_Gravel (corroboration)