Stage One: A general rising of discontent at the existing political leadership. This is distinct from mere generational change; one of the best examples is the demise of Southern Jackass authority within the party from 1967 or so until 1974 (when, as is the nature of things, they went pear-shaped; and yes, there's a specific reason for this Briticism). This is usually exacerbated by the party leadership being in the hands of people who are seen as, well, apparatchiks who could not, themselves, be elected to a contested political office; the current HNC chairman is an excellent example.
Stage Two: Ideological purity begins to shift from long-standing party beliefs to newer, and usually moralistic, pass/fail tests that reject nuance. The Heffalumps are now shifting away from "strong on defense, lower taxes" issues toward "no government intervention at all, hyperconservative Protestant morality." I'm just waiting for the first time I hear one Heffalump call another Heffalump — probably a very conservative one, like John Cornyn — "objectively liberal." Damn, it looks like I'm much too late. Schade.
Stage Three: Opportunist fellow-travellers begin to use the new, extremist movement to get themselves into power, feeling free to ignore their own pasts and the "new" ideology they're supposedly supporting. For a time, the internal solidarity of the extremist movement will hold up, even to the point of getting some of its members elected to office and perhaps onto top-level ballots. Perhaps the most obvious example of this is the figure-headedness and shenanigans behind the 1972 Jackass Presidential ticket: As extreme as McGovern was portrayed, he was nowhere near as extreme (based on his actual voting record in the Senate) as many of his supporters... who were more than happy just to be done with the overt racism of the Southern Jackasses (while imposing an equally pervasive Model-T racism of their own), and thereby ignored everything else.
Stage Three is the most dangerous stage for the polity — not because it risks putting extremists in office so much as it risks getting extremists into essentially unreviewable management roles immediately below the elected/confirmed-by-the-Senate level. We recently had more than a glimpse of this in the Department of Justice, and nobody knows how much has remained below the surface. (No political party is exempt here.) We're somewhere in the middle of Stage Three now for the Heffalumps. I'd argue that that party entered Stage Three around 2003, meaning that — if the historical record in American politics is followed — we're getting close to, or perhaps are at, the saddle point (PDF). And since the implication of a saddle point (in mathematical physics, physical chemistry, and game theory) is that movement away from the saddle point is of unpredictable direction and magnitude, we're in for a good time....
Now, what was that line about those who don't know/understand history being doomed to repeat it? And what might that have to do with the antiintellectualism endemic in both parties' apparatchiks (and yes, the repetition of a pejorative term for Tsarist and Soviet government officials is with malice aforethought)?
The truly masochistic are invited to apply the above to the publishing industry.