Their politicians are that stupid, but I have a hard time believing that their electorate would be. They would be an independent, earthquake prone nation with no water supply, natural resources that were exhausted a century ago and an economy that was entirely dependent on the country they had just voted to leave.
All the talk of secession proves is that there are as many idiot liberals as there are idiot conservatives.
Water supply and natural resources wouldn't be an issue for them, as they just import it. The US wouldn't switch off the taps on California - they'd just trade for it, like the USA has traded for oil with the middle east and so on.
Independence doesn't mean being like a video game and collecting resources to survive.
Again though, I couldn't actually logically argue for it myself, but my point is that it could become so emotionally tempting as a result of a lunatic Trump administration that a state like California would feel they had no other choice. It'd be like abolishing guns out of the blue - Texas and the likes would be clamouring for the same thing, and if it did go to referendum they'd be highly tempted to secede on that sole basis alone.