Do you think Kushner cost him the election?
Trump would probably have done better with Ann Coulter as advisor. As it is now, from what I read, Trump lost a bit of the white male vote, all other groups voted for him in greater numbers.
I think Kushner may have helped Trump an insignificant amount with the black vote, which is only 13% of the population, but hurt him a little with his core supporters. It's really too hard to tell what support Trump actually received until voter fraud is revealed insignificant or significant enough to change the election outcome.
Ann Coulter or Michelle Malkin as far as well known vocal Republicans who have adapted well to a post-neocon Republican party and could serve as Trump's compass and conscience. Ironically, two women stand out as having the most fortitude.
Just from anecdotal evidence, I've seen many who voted for Trump no longer support him based solely on his Israel-first agenda. Israel's now the winner of every US election regardless of the winning party. The 'gentleman' Trump ceremonially gave 'the keys to the White House' just declared his allegiance to Biden/Harris before Biden has even been declared the winner. Trump might a well be the USS Liberty as far as Netanyahu is concerned. Zero loyalty or empathy for the "other", just who 'in the moment' can serve him.