Some Republicans believe that a significant percentage of Trump voters are Democrats and independents who are only voting Republican to vote for Trump. Massachusetts provides some evidence. Only Republicans or unenrolled voters were allowed to vote in the Massachusetts Republican primary. So 16,347 Democrats switched from Democratic to unenrolled and 3,455 of them became Republicans. These people were likely largely Donald Trump supporters. It's been presented that Republicans are telling the party establishment what they want and that's Trump. Except these voters aren't Republicans and they've decided to tell a political party they're not a part of what they want. They're telling Republicans they need to change their views to what they think.
That's allowed, but these voters haven't supported the Republican party in the past and likely have no intention of supporting the Republican party in the future. They dislike the Republican party and certainly wouldn't support the "establishment candidates" the party runs. I know political parties get a bad rap but they exist for like minded people and candidates to have a common brand. The Republican party has a brand. Sometimes people like it enough that the party wins elections. Other times it doesn't.
If you don't like political parties, you don't have to join one. If you're a candidate who doesn't like where a party stands you can run in another party or as an independent. It's like a stranger coming to your home and deciding to redecorate. You still have to live in your house. The stranger won't. The Trump supporters have decided to latch on to the Republican party and now are upset that people who don't agree with them politically, who've been in the party for years, don't want to provide their party apparatus to his candidacy. The media is presenting the situation as those who want to change what the Republican party believes are some sort of grassroot revolt and those who don't as establishment unreasonably resisting. There has been a lot of grassroots Republican support in the past. If Trump wins you'll see a lot of resistance. The winner in all this is the Democratic party. That's not because people like what they're offering, but because the opposition is experiencing a hostile takeover.