The scale of the opposition would be difficult to quantify - the whole reason liberals hand power to fascists in the first place is to violently suppress dissent against the status quo, after all.

Italy gives a clue, however - almost the entire north of Italy was liberated by antifascist Partisan movements (before the US and UK suppressed them, of course.) The same thing happened in Greece - and Greece had turned fascist even before Italy and Germany did.

So yeah… Hitler’s (supposed) “popularity” should be viewed with the same suspicion as Putin’s.