1) Republicans in office wreck shit.
2) The Public gets pissed and vote in Democrats [Though anymore it takes nightmarish Republicans and their policies to get people to do this].
3) Democrats begin to govern but people feel the pain from the messes the previous Republican administration made and begin to ignorantly blame Democrats for something Republicans wrought.
4) Democrats work their asses off to clean up the economy, get things back on track, implement good policies that stabilize and benefit the majority of Americans.
5) The Public is convinced, with the help of the media and Republican messaging, that the messes that still linger and were wrought by Republicans are the Democrats fault [because thinking is hard].
6) Public votes Republicans in again.
7) Republicans keep campaigning after taking office because they are inept and don't know shit about governing. They then take and get credit for the previous Democratic administrations good policies which are now being felt by the public in general.
8) Go back to 1) and repeat
This cycle may only stop if the public votes in Democrats for more than two terms and it would likely take more terms than that to see what Democrats could really do. People would finally understand what they had been missing out on for decades due to their ignorance.