I'll take a look at your article.
But how have both parties moved to the left? Rhetorically? The US is the outlier among developed countries in so many economic and social ways because the US has moved to the right, not the left. The US isn't a functioning social democracy, because its individualism makes it susceptible to conservative social Darwinism (libertarian egoism).
This is why progressives feel they have to be incrementalists, because they're walking uphill or going against the American grain. The US moved to the left with the New Deal and with Johnson's Civil Rights Act. After Carter, both parties abandoned progressive principles since the business community got involved in steering the discourse and shifting the Overton window. That led to neoliberalism's (free market ideology's) capture of the Democratic Party.
Sure, there are recent radical left-wing movements (Black Lives Matter, Me Too, and so on). But they've made for only token changes in the Democratic Party, forcing Biden to pick many women and minorities for his cabinet, all of whom are neoliberal centrists or old hands in Washington (meaning they're realists, not idealists).
Trumpism has a number of causes, but I'm talking here about a radicalization of the GOP that goes back at least to Newt Gingrich and to the rise of Fox News and right-wing talk radio in the 1990s.
The issue here is more like climate change than weather patterns, in that it's about a larger dynamic, a systemic boxing in and perhaps dooming of the GOP.