Its different with the Democratic party for several reasons. In the Republican party, you have a large group of people who do not accept the majority view of what is acceptable in our society, and they feel they have been forced out (in my opinion rightfully so) of the national discussion. I am talking about racists, bigots and religious zealots. The elected officials in the Republican party (mostly educated people who are not bigots or zealots) know that to accept this group is to marginalize the party and turn it into a regional power without national influence. Trump plays to these people, while trying to keep a foot outside of the bigot arena. He can do well with that in a primary campaign, but in a general campaign he will have to moderate and bet on short memories. If elected he will have a hard time governing from both places and the bigots will likely be even more pissed off when Trump abandons them.
On the Democratic Party side, the structure of the party is very different. The insiders have more power and thus an outsider has a harder time doing what Trump did. The Democrats have their share of people who push for ideas outside of the mainstream but for the most part the Party has been able to keep them under control by promoting the idea of incramentalism. Telling those who are ready for more radical ideas to be patient, that change comes slowly and to look at the progress we have made by taking one step at a time instead of trying to go too far too fast. Its easier to be the party that promotes slow change than to be the party that demands we return to a fictionalized past. Its impossible to return to a fictionalized past, because it never really existed. Its easier to make slow change to a place that was not defined in the first place and will never reach the ideal, but slowly make progress toward it.
I'm not calling all Republicans bigots or racists or Zealots, but there are plenty of them that are attracted to the Republican party and they are like a fly to a light with Donald Trump. This is why you see the more educated and more intelligent Republicans revolting against Trump. The problem with Trumps future campaign is that thus far he has done a great job of keeping one foot in each boat, but the further into the future he gets the more those boats drift apart. It will be interesting to see if he can keep two groups together long enough to get elected.
