The Democrats control Congress with razor-thin margins, the Supreme Court has been stacked with Trump Nominees, Republicans can keep stonewalling in Congress unless the Democrats take a huge gamble and get rid of the filibuster, Republicans still control the majority of state houses and therefore also have a huge influence on the districts used in the next 10 years, and even if they don't, the existing districts are heavily gerrymandered in the Republican's favor.
Not to mention that Trump didn't get barred from running again and the Electoral College is still in place despite the fact that it literally failed in it's intended function in 2016.
Now please tell me again how the Democrats hold all the cards.