Abstaining or voting 3rd party to "make Dems listen" doesn't work. If anyone thinks they can play Mexican Standoff, you can't because the Dems have an out: the center voter. Every time they lose, they go to the center to find voters.
And remember they need all 3 of presidency, house of representatives, and senate to pass pretty much anything. If they don't have all 3 they will go to the center to find voters. Some people call this rachet effect, but really they're looking for voters. Want them to stop 'racheting'? Then give them consistent and overwhelming victories.