I guess its a philosophical question... at what point can a "strong majority" of anything be considered "virtually everyone"? If its more than 80% (your current suggested threshold of the republicans who support Trump), then what about 90%? What if every republican liked Trump, except for one lone holdout in one small corner of the U.S.? Would it still be accurate to talk about "all republicans" then, or is one voter enough to claim "oh, not all republicans feel the same!"
And how much does actual opposition factor in? After all, you can claim "not all republicans support trump", but opposition to Trump hasn't caused all the non-Trumpers to leave the party (nor has it prevented Republican congress critters from voting for a tax plan supported by Trump, or blocking any of Trump's nominees). Granted, under normal circumstances you wouldn't expect someone to leave a political party just because they don't support the leader, but Trump is not normal... and having a racist orangutan as president should be justification enough to leave the Republican party.