Dems have moved to the right for decades since Clinton's attacks on the working class with NAFTA. Obama called himself a moderate republican and governed like it.
So your assertion is that the arc Clinton -> Obama -> Biden represents an increasing rightward shift in the party, is it?
Do you know what would have happened to a self-described socialist who tried to get the nomination in 1996, or a Palestinian congresswoman who talked about "From the river to the sea" in 2008?
Read "Listen, Liberal" by Thomas Frank for a detailed description of this.
I genuinely started looking for this, because I was curious what it had to say, but then I reread how you summarized it and concluded I probably don't need to.
The US is always at war in at least one place somewhere on earth, and has learned from painful experience how easy it is to ratchet a conflict up into a bigger deal than it needed to be and how difficult to ratchet it back down, so they pay close attention now to when they’re crossing certain lines especially when nuclear weapons are involved.
Put it another way, all the nations of the world all go to the same bar, and a lot of them have guns and split personalities, and they spend every night playing cards and cheating and there’s always at least one fist fight, and somehow it’s been about 75 years since anybody got shot.
https://sais.jhu.edu/kissinger/programs-and-projects/kissinger-center-papers/escalation-management-ukraine-response-russias-manipulation-risk