Actually Romney's biggest gains tended to be among white bourgeoisie types in upscale suburbs in the North. You know folks like me, who voted for Obama in 2008 and Mittens in 2012 - precisely the type of voters who will never, ever, vote for Trump. And in those years I lived in Orange County, CA. My burb trended about 5 points to Mittens, or something like that, vis a vis McCain, meaning the swing was about 7 points.
I can't speak for Romney's gains on a regional basis for specific groups of whites, but in California there is no way Trump is going to score out of the park among whites like Mr StatesPoll said.
This guy has the most biased outlook I've seen. He just randomly pumps up Trump's numbers to ridiculous levels because he thinks him getting crowds translates to unrealistic gains everywhere while not alienating any white people at all. Trump is never going to get close to 60% among whites in a general election. Not with the white no-college share of the electorate dropping heavily every 4 years.