According the traditional model, only the opposition party can introduce realignment. In the US the New Deal paradigm was introduced by the Democrats and followed by both parties so that even Republican presidents governed like moderate social democrats focusing on government services.
The Republicans introduced Reaganomics (aka the Reagan Revolution) after Democrat Jimmy Carter tried and failed to introduce some elements of it. It has been the dominant paradigm since and is perhaps better called neoliberalism a. According to the model the Democrats need to introduce the next paradigm which will be more egalitarian and communitarian, serving capital less and citizens more.
But… that’s not what’s happening. The Bernie Sanders (realigning wing) of the party is being frozen out in favor of Elisabeth “Hillary-lite” Warren a fanatical neoliberal who, like Hillary Clinton uses cheap identity tricks as camouflage. Similarly in the UK Labour has become the open party of neoliberalism through its adoption of Open Borders idealism and disengaging the idea of citizen participation to opening elections to all residents.
The parties that should be leading realignment are leading the resistance to realignment. I don’t think that realignment away from neoliberalism which everybody but a small elite is thoroughly sick of can be stopped. But the transition can be relatively smooth (as in the Roosevelt and Reagan cases) or it can be a train wreck with vast human costs. The Democrats and Labour have disabled the brakes and don’t even see the landslide blocking the tracks. I think it’s gonna get a lot worse before it gets any better…