Both the Marxists in the Soviet Union and the Nazis in Germany tore down their countries and rebuild them in accordance to their tyrannical ideologies. It’s a stretch to call regimes that brought radical change conservative when they clearly not for preserving anything from the previous regimes.
In both cases, they co-opted popular left-leaning movements to engage conservative voting bases. They combined these popular movements with nationalist conservative ideologies to garner wide appeal amongst conservatives.
After winning, they then used their momentum to tear down institutional checks and balances to make sure they would hold power indefinitely, even if their support started to wane. Conservative support, in both cases, remained strong for many years, resulting in the deaths of millions of innocent non-conservatives.