Mathematically, Nader did cost Gore the election in Florida.

Stein did cost HRC the election in Michigan in 2016. She received 30k more votes in 2016 than in 2012 and the lost to Trump in 2016 was 17k. The GP candidate did not suddenly become more attractive as a candidate other than as a protest vote against Clinton.

HRC wasn't forced on anyone- she won the primaries as did Biden.

As long as my fellow progressive (and Bernie supporters) cling to the 'we got robbed' mantra (which gave Trump ammo for fraudulent election) progressives will be hard pressed to evaluate what really needs to be done to win.