(Link to the electoral maps from 2008 to 1972)
In this very short section of history you’ve selected here, it’s because they’re cleaning up after the Republican administrations that have made a giant, giant mess.
Like when they add $5,400,000,000,000 to the debt? Or have unemployment at or above 8.0% for 43 months straight? Or when they unrepentantly sell firearms to drug cartels?
Exactly like that but with one key difference: there’s no need to mutilate the facts. Like when Bush turned a $5 trillion surplus into a record deficit, like when Reagan unrepentantly and extra-constitutionally sold arms to Iran to fund anti-government Rebels in Nicaragua. And also, Watergate, which kicks off the era you highlighted.
And that’s leaving quite a bit off the list :)