A minority of fascists can orchestrate a legal coup against a government that is ostensibly governed by majority rule. Specifically, no known system of government can withstand 1-in-3 people actively betraying that government.
This is a consequence of computer science research into managing consensus in a distributed systems of machines. One important result of distributed systems research is that no known distributed system can withstand a Byzantine fault where 1-in-3 machines actively work against the consensus protocol.
If you view our system of government as a distributed system (where the "machines" in this case are people), then fascism is a Byzantine fault in that system. If fascism gathers the support of 1-in-3 voters, then no system of government can maintain its integrity against that onslaught.
The reason why Byzantine faults can undermine a system without a majority is that they assault the very protocols that are used to ascertain consensus. For fascism, that includes:
- Corrupting the administration of elections
- Exploiting legal loopholes or grey areas
- Installing partisan judges
- Spreading misinformation
This is the reason why you'll often see support for fascist administrations hover just above the 33% mark, because that is the threshold where fascism becomes politically viable.