I read an article today where the author suggested the the Democrats should adopt the British model and form a shadow cabinet to oppose Trump's agenda: https://www.washingtonpost.com/opinions/2024/11/11/shadow-cabinet-democrats-opposition-trump/
The reply comments were interesting. Quite a few of the ones I read were more concerned that calling it `shadow' made it sound like a suspicious deep state organisation rather than a competent and informed alternative governing body. Others thought that it would just be a leaderless group, but logically it would come under the direction of the minority leader of House of Representatives - effectively the leader of the opposition.
It's largely because the USA doesn't have something like a shadow cabinet ready to take over, that they have this shambolic two month period when the incoming administration rushes around looking for people to fill essential posts while the outgoing government twiddles its thumbs.
I suppose that even if they thought it was good idea, the Democrats wouldn't have the office space, support staff or funding to set up such a body.