Actually it would not work the way he'd expect. Two of the States would be well left of center an produce 4 Democrat Senators. The 3rd one would be purple like Oregon, although initially a reddish purple, but likely turning blueish very quickly for the same reason Oregon did, a lower tax haven for Californians. So you'd likely add 3 Democrat and 1 Republican Senator.
But here is the blunt truth, there is no deep division in California expect in the Jefferson Movement; not sure they are even a majority in the counties they claim, but they are significant in the "Northstate". This movement has real roots and a long history and actually has a slight chance of someday happening. (Some issues for sure have to be ironed out, but most of us would say good luck, you're on your own, and the actual counties that would split may be slightly different ... can't see Del Norte or Humboldt remaining and would be surprised if the Sacramento suburb dominated Placer split or some of the farther south mountain counties split, as they have no access to to the North such as Amador and Calaveras)
http://www.latimes.com/local/lanow/la-me...story.html
The demographics are enlightening:
http://www.latimes.com/projects/la-me-th...on-census/
Jefferson: 1,738,337 people, 73% White
California*: 38,071,356 people 37% White
* California numbers not counting Jefferson (numbers taken from Jan 1, 2018 census estimate; total population was 39,809,693, but now maybe >40m as I write)
It'd be Trump country for awhile anyway, much like Idaho. But it would have it's liberal bastions in Chico and Humboldt, and once a State Capitol was established, likely in Redding or Shasta, that would start to be a destination for Californians to move to much like Portland and Seattle are now, changing the demographics over time.
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But as for the ballot measure, the divisions the authors of it see are invisible to those of us living here. Conservatively, you could see 4 or 5 of the remaining GOP House seats flipped this fall. It's been a very long time since Orange or San Diego counties were majority white. This will get voted down maybe by a massive margin, >75% is likely. Amazing who insane the GOP looks in California.