Can't have presidency, house and senate and go to the electorate in 2 years talking about Republicans. That's how you get washed
There's really nothing they can do. Once you accept the fact that the democrats are the enemy of the republicans but the republicans aren't the enemy of the democrats it all makes sense.
The democrats and republicans overlap on certain things and the republicans will work together with them on those things. Everything else the republicans block, obstruct, and derail. Those things they stop tend to be the things that help the general public at large over the rich elite. Because the republicans are united entirely when they get power they push their pro rich elite agenda through smoothly. That's all they really do. When the democrats align they help that cause and when they don't they get steamrolled and blamed for the failure to set policies that help everyone else.
In the end the democrats are held to a standard and expected to actually govern in a way that helps everyone. The republicans aren't held to any standard and can do whatever. When the republicans mess up everything really bad people run back to the dems briefly but that's always short lived. Mostly because the dems aren't fully unified and because they can't count on the republicans for shyt.
This is unlikely to ever change. The republicans have a large block of low information voters that aspire to be more than they currently are but fall short. These voters easily fall for the propaganda the republican party pushes out. The dems aren't getting those voters.