Biden didn't win by 4.5% He won by the cumulative margin of victory in a few states to get 270.
Ehhh millenials are the most liberal because they are the youngest I imagine. Anyway, this stuff all ebs and flows anyway. Half the game is just capitalizing on the other team's mistakes and Dems are no strangers to making big ones.
We see the narrative anytime the GOP loses a Presidential election. "Is the Republican Party on its Deathbed?" Parties adjust. Does the GOP have work to do? Yep.
Due to the vagaries of the electoral college the partisan advantage vis a vis the popular vote flips from time to time (Kerry almost won the EC despite losing the popular vote) because if this tracking the popular vote is more accurate in terms of where things are trending (like tracking yards for/against. 2012 ND was undefeated but advanced stats had them barely top 10).
Millenials may trend more conservative, but consider 25 and 35 year old vote identically. This is very odd. People tend to make a Pepsi vs coke delineation between the parties after their 1st 2 elections. People who came of age under eisenhower vote more republican than those in the age of Kennedey. Reagan is really the last president that had a positive partisan effect for Republicans. Those people are 50+. Clinton had a positive impact for dem branding, GWB was awful for repub branding, Obama loved by the young, Trump hated by young voters.
Additionally the country gets more college educated and less white over time. This crushes the republican base. Under 40 repubs additionally believe in climate change and are more open to government involvement in the economy.
I'm of 2 minds of where this can go. Throughout our history we tend to have one party dominate with either a flip to the other or a contentious period of polarization. It was Dem vs Federalist. The Federalists got on the wrong side of immigration, lost their leader to a duel and fell apart. Then it was the dems vs. The whigs. The Whigs were torn apart by divisions on Slavery. The repubs dominated from the civil war through Grant's presidency. Then the Gilded age was really a hyper partisan time with no consensus. Republicans came to dominate from 1900 till Hoover (Wilson won but due to a split repub vote) The Dems really dominated up till Reagan after the Depression.
Every repub president offered a slightly moderate version of the new deal/was ok with big government. Then with Reagan came a small government/Republican consensus. Even Clinton was a moderate caretaker of the Reagan consensus. Since 2000 we've been trending towards a Gilded era style polarization. The question is what is the new consensus and do we get another 20 year era of a New Deal or Reaganomic consensus. It seems there is a big government consensus coming and the question is whether the R's adapt or are happy being a dominant regional party