January: Biden
February: Biden
March: Biden
April: Biden
June: Biden
July: Biden
August: Biden
September: Biden
October: Biden
November: Biden
December: Biden
January: Lead starts to disintegrate.
February: Bernie gains momentum/becomes frontrunner.
March: Biden miraculously skyrockets back to the top after winning 1 conservative state. All rivals drop out.
Biggest difference really is that the Republican party is smarter and understands power. They threw everything and the kitchen sink at Trump but eventually realized that he was their best shot and the voters loved him for saying the quiet parts out loud.
The GOP accepted the radical Tea Party back in 2010 when they realized that those bat shit crazy fundamentalists were good enough to swing state elections for them and could bring them back into power. Look at the Dem response to Occupy Wall Street. Look at how they treated Black Lives Matter back in 2014-2015. Dems refuse to change the course of their party. They rather uphold the status quo instead. Historically, that party has had to be dragged, kicking and screaming the entire time when it comes to anything left based.
There's a huge age gap among Democratic voters, and the party itself is ruled by fossils and deadeyes careerists like Mayor Pete who just parrot what the fossils say/do. The Dems just take younger voters for granted and tell them to sit down and shut up because it works, just like an abused kid being told by the parents "it could be so much worse!"