At least 45-46% are still going to vote for him no matter what. That's the sad but hard truth.
Any Republican Nominee will get 45-46 % because of the increasing polarization in the Country.
Even John McCain got 46 % YET he lost the Electoral College in a landslide.
If 57% want to get rid of Trump once and for all, perhaps just vote for Biden in the GE, if you can't beat Trump in a primary?
Except 70% want to get rid of Biden once and for all too
https://thehill.com/homenews/campaign/3771024-poll-70-percent-of-voters-dont-want-biden-to-run-for-a-second-term/and that includes 44% of Democrats who don't want Biden to run again
https://www.pbs.org/newshour/nation/most-democrats-dont-want-biden-to-seek-a-2nd-term-poll-saysIf you want to talk about Trump's unpopularity, you should also be mindful of Biden's unpopularity