Apples and oranges.
First of all, I don't think Bush had any major challengers in 1992 except for Pat Buchanan. Even still, Bush won every single primary and caucus by a landslide. Buchanan only got the attention he did because he was the only main challenger. I think New Hampshire was Buchanan's best showing and it was all downhill from there.
Then we had that Ross Perot excitement during June and July.
Trump leading virtually every early poll by a wide margin in a 17-man race is clearly unprecedented and can in no way be compared to Pat Buchanan's 1992 run.