If something can be easily put in place by a President's executive orders, it can be easily removed by another one's. That is why if we want things to stick, we should be pushing them to be laws, not depend on the mercy of one President's proclimation to the next.
If people do their jobs, he will have 4 years to cause havoc as the President. While that is happing, the Democrats need to be campaigning on issues the people need solutions to and working to put more of themselves in the House and Senate, preparing for the next Presidential election. Grooming up candidates that will have a good chance of defeating the Republican canidate. If they can get the numbers in both the House and Senate, they can then craft into Laws old executive orders they want to protect.
The above would require them to also cease the focus on having wedge issues, but instead focus more on creating and enacting solutions. They do that, then they may just be able to draw more people back into the fold and off the couches next Presidential election.