The Republicans have a Trump problem, especially with independents that they refuse to acknowledge. Yeah, the democrats have a mouth problem with slogans that don't mean what they want to say. I would say you're correct on the slogan, "Defund The Police," costing the democrats 13 house seats. So both parties today have their problems.
But I'd say the democrats problem is dwarfed by the GOP and Trump. At least today.
Trump has reportedly been telling people he'll be 'reinstated' by Augusthttps://news.yahoo.com/trump-reportedly-telling-people-hell-133110019.html
The man is deranged. Now if I were a democrat, I'd want his followers to just keep following him as that would tend, in my opinion, to keep the independents in the Democratic column.
It certainly wouldn't hurt if the Democrats to put a sock in AOC, Omar, Tlaib etc mouths as they say such outrageous things that tend to drive indies away. It is also very hard to convince independents that those three aren't the spokespersons for the democrats as they get plenty of air time and independents don't pay much attention to daily politics if any at all.