Trump in perspective -- will he stall out at his current 25%

We're all so intrigued by Donald Trump's running away with the primary (for now, anyway) that we may be losing sight of what it actually means.   

Yes, he's way ahead in the polls at 25% -- but that also means that 75% are not choosing him.   The question is:    Can Donald Trump expand his appeal, or is this as much of the electorate as he can attract?    It's hard to assess this when there is such a large field.

Ralph