American Liberals are a different thing from those who subscribe to (non-American) liberal ideology.
Democrats have a really low bar to score. "Not Trump" is shockingly low. Leftists are in agreement, "not Trump" is better than "Trump".
I really don't think the democrats need to do much at all to convince the left, besides remind everyone how fucked it was four years ago.
I think it's more important to prevent people migrating to the right (as we see with GenZ Andrew Tate fans), and pull in as many moderate right-wingers as possible.
It seems impossible at first glace, but I've seen viseos of republicans openly trying to convince their peers that Trump deceived them. It gives me a sliver of hope.