You may not understand what the Republican base is.
I'm sure I don't fully understand it. But I do know a lot of people that by historical standards would be considered to be in it. And I know a lot of people who by historical standards would be considered to be "insurgent" Republican base people. And NONE of them like Trump.
I think an interesting research project would be to poll people and identify people who were registered as Republicans one year ago and ask them if they would like for Trump to be the nominee or if they would prefer that he not be. I suspect that the overwhelming majority would prefer that he not be.
I think Trump is benefitting from a lot of people who have not traditionally been Republicans voting in Republican primaries for him. I even saw a liberal radio talk show host on CNN the other day saying that about half of his callers who say they voted for Trump are Democrats who voted for Trump in the primary because they want him to get into the general election as they think he is the easiest candidate to beat. And we have all seen reports about how Democrats are switching to Republican so they can vote for him in the primaries.
I really don't think this is a "Republican base" thing. Sure, some members of the Republican base are undoubtably voting for him. But I suspect that if only people who have historically been members of the "Republican base" were voting he wouldn't be doing so well. I really do think that, whether establishment or insurgent, a substantial majority of people who have historically been Republican do NOT want Trump to be the nominee.