The claim is false, as long as they are unable to change the form of the government they tend to flame out and lose support quickly, because there's not that much substance behind their populism. They tend to have no real plan that's why different from a typical warlord, just on a slightly bigger scale.
Unless they go to war...
The real issue is that nobody with any degree of power really cares.
Ok, so the states fall, but not before existing for at least a generation and in some cases effectively an entire working life:
- Francoist Spain: 40 years.
- Pinochet Chile: 17 years.
- Salazar Portugal: 36 years.
If you were 22 when Pinochet took power for example you didn't see the end until 39. Your best years lost. And that's the "lite" version. (I ignored Italy because of WW2)
If the US MAGA contingent gloms on to this fascism malarkey by anointing a true believer after Trumps inevitable death (he is pushing 80, after all) we would be looking at decades of loss.
On the other hand, Pinochet in Chile held an election in 1988. The choices were to keep him as president or replace him with a constitutional government. He lost (55% to 45%) and he stepped down, allowing a democratic government to replace him. This negates the main thesis, of a 0% success rate in stopping fascism.
OP Refuted by:
Italy (Mussolini’s Fascist Regime)
Spain (Franco’s Regime)
Portugal (Estado Novo)
Chile (Pinochet)