Outside of making their messaging more effective and not wading into so many bullshit culture war traps laid by the Republicans, I do not think the Democrats need to do much else over the next 18 months other than lay low and let the GOP punch itself out. The Democrats should be a very vocal minority party, voting no on literally everything and spending all day every day screaming about how awful this Trump economy truly is. The policy aims of the Trump administration are so breathtaking with bad and so extraordinarily unpopular to everyone except for a small part of the ultra MAGA base, the Democrats won’t really have to do anything other than what I have outlined above for the next 18 months until the midterm. The Trump administration is already taking body blows and scoring own-goals and we are not even two weeks in; they completely buckled and back down like enormous pussies today with the budget free stuff, and the blanket pardon of violent January 6 convicts is deeply unpopular even among conservatives. There is going to be so much ammunition and cannon fodder Kratz if they can just grit their teeth and sit back and let Republicans Republican.
Aside from Trump actually not winning, this has been a best case scenario so far if your ultimate aim is the demolition of the Republican Party. The Trump administration was a lame duck from the moment it was inaugurated last week, they basically have 18 months until one or both houses of Congress, and Trump eked out smallest popular vote win in generations but is arrogantly behaving as if he has a mandate.