Democrats must stay steadfast behind Biden in order to defeat Trump. One bad debate doesn't cancel out everything Biden has accomplished while in office, his principles, and — possibly most importantly — his previous experience beating Trump in 2020. His post-NATO conference press conference answers showed he still has the mental acuity for the job. Democrats don't need chaos; they need to back their nominee.
If anything, the assassination attempt on Trump makes it more urgent for Biden to get out of the race. Trump's popularity is sure to soar, while Biden's dismal approval ratings and terrible polling in the swing states are only going to get worse. If defeating Trump is the existential crisis that progressives know it is, Biden should do what's best for the party and the country.