It's not all on him. Trump claimed election fraud in 2016 and again in 2018 and did absolutely nothing to launch criminal investigations that would lead to charges and trials. If Kushner didn't deal with it then the same can be said of the President.
Yes, but if you delegate to your supposed senior adviser to oversee the campaign, that’s on the sr. adviser to handle. Trump had a country to run.
Having been complicit in the Kushner handling all along is too likely part of Trump playing a role all along too, I grant you. Unfortunately.