The Left Wing thought they were in a position of dealing a final death blow to the right, and to the Republicans. They believe that Clinton, was the final tally needed, for a total, and insurmantable victory. They have won almost every battle, besides some off-year congress elections, and demographically, it appeared like this would continue.
They were wrong.
Now, the left, and the Democrats, have lost the Presidency, the House, the Senate, the Supreme Court, they've lost the majority of Governors, and the majorty of state congresses. They now only hold total majorities on the coastal states, and even the rust belt has turned red.
If the Democrats fuck up a bit longer, if they double down, if they choose Keith Ellison, a Muslim bigot, if they run another, "insert oppressed minority" as their leader, they may be totally done.
The Left got cocky, they thought it was over after their recent victories, after having the media, and after the right looked weaker than ever. They now find themselves squabbling, with almost no power, and with the assurance of another 30+ years of a conservative supreme court. Meanwhile, the GOP redefines itself as a libertarian-conservative-nationalist party, instead of a Christian-authoritarian-nationalist party. If the left fucks up, they will descend further, and I wouldn't be surprised if they never hold higher offices again. The right, unlike the left, is not so weak. And as the left is so fond to say about themselves, The arc of history bends towards justice.