Chapter 2 of his 1991 book The Nature of Fascism provides the concise definition and describes structural weaknesses of fascist movements.

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Generic fascism consists of three elements:

1. The core of the movement contains a palingenetic myth (death/rebirth). They see society as decadent and liberal, and on its way out. That by burning down the system, their mythical utopia will “rise from the ashes like a phoenix”.

2. It is a populist movement with a charismatic leader who typically exerts a “top-down” populism where decisions of “the people” are made by the leader. The leader usually stresses a “meritocracy”, but ends up placing incompetent loyalists into positions of power.

3. The movement’s ultranationalism goes “above” and “beyond” traditional and legal forms of politics. It rejects Enlightenment humanism and liberal institutions (things like rationality, logic, the rule of law)

Structural weaknesses of the palingenetic myth: The movement is prone to factionalization due to the vagueness of the utopian vision. It also cannot sustain itself without continually designating new enemies from within and without, because the utopian vision can never be realized, there must always be a new enemy hindering its success.

Structural weakness of populist ultranationalism: The movement cannot survive without its charismatic leader. No matter what, everyone grows old and dies, even dictators.