I think that BBC article is based on what the Wall Street Journal wrote today
"Donald Trump Is Starting to Look Like an Independent Candidate
Travel around the country speaking about the election and you’ll frequently get this question: Can an independent candidate make a serious run for president?
We now essentially have such an independent candidate. His name is Donald Trump.
So the new questions are: Is it possible to win an election that way? Perhaps as important, if a candidate prevails in such a campaign, could he govern effectively afterward?
Increasingly, Mr. Trump and his unshakable core of supporters are breaking away from the party hierarchy."
www.wsj.com/articles/donald-trump-is-starting-to-look-like-an-independent-candidate-1476115731
It is essentially correct. Trump never was a Republican in the sense that the rest of them are and he has overturned their sacred cows and the Republican voters are with Trump and not with them. Trump hijacked the Repubican Party, challenged, defeated and mocked their icons and is drawing support from ordinary Republicans, independents and even some Bernie supporters. Trump is the wrecking ball independent who will clean the system up.
"Donald Trump boasts of war with Republican leaders: 'The shackles have been taken off me'
www.independent.co.uk/news/world/americas/us-elections/donald-trump-shackles-republicans-paul-ryan-twitter-us-election-2016-a7355996.html
The more Trump challenges the Republican Establishment, the more popular he will become because most people have no love for the political class.