I'll take a whack at it for you!

The DNC chairman is not a politician that leads the party in a "public facing" sense, their job is more management with duties like coordinating all the state party's activities, e.g. setting goals, organizing (meetings, the conventions, etc), finding candidates to run, and raising money from donors.

There is no official leader of the party when the party doesn't hold the presidency, someone may be acknowledged as the unofficial leader if they are dominant in intra-party politics (like Trump was the last 4 years for the Republicans). When there's no clear leader, often after a presidential defeat, the party will regroup and make general plans until a leader emerges.

So we're in the worst position to combat Trumpism, no clear leader nationally with and no unified plan. The Democratic congressional leaders aren't accomplishing much (IMO) and any blocking of Trumpism is slowly happening in the courts. Meanwhile every day has a new set of disasters, Trump's dropping in the polls is the only good news I can see.