What has proven most effective is in fact a strategy, not a movement.
Progressives of the socialist Left have learned that they may succeed in their ambitions not by promoting an agenda, but by controlling the public language.
The chief tactic employed in this effort has been the purposeful and by now, successful redefinition of important words such as "justice", "fairness" and "rights", so as to change public understanding of what they actually mean. By controlling the language, a movement may in time convert the public's comprehension, and turn private activity into the service of nakedly political ends. In essence, by controlling the language, one can alter the public's idea of Reality.
Crucial in this effort has been the Progressive march through the institutions of public life: the educational establishment, the news media, the arts and entertainment centers, faith-based organizations, and the government bureaucracies.
The Left now largely controls all of these in America.
A closely-related and equally vital tactic has been the use of epithet in order to define and demonize the opposition. Terms such as racist, sexist, bigot, homophobe, warmonger, Nazi, and others have been employed both intentionally and indiscriminately for many years now.
And now that the Left controls the language through its dominance of social institutions, it is sufficient only to accuse, not to prove. Accusation is now commonly held as proof of guilt. The burden has shifted to members of the accused and disfavored groups, and in favor of those groups the Left champions - in fact, manipulates - in the service of its political agenda: the consolidation of its power, and the accumulation of unearned wealth with which to purchase the loyalty of its client groups.
The result has been a fragmentation of America into tribal and geographical identities: wealthy coastal elites, dependent urban constituents, and culturally alienated members of the disfavored groups in the great center of the country.
Where we go from here is uncertain, but it is certain that absent a change of course and the rise of new leadership in opposition, the center will not hold.