A vote for Johnson is only a half vote against Trump, while a vote for Hillary is a full vote against Trump.
Bullsh**t. A vote for Johnson is a vote for Johnson. I probably won't vote for Johnson, but I certainly won't vote for Clinton or for Trump, and you may not count my opposition to Trump or to Clinton as half of anything. It is full-on, raging opposition, just as those who will vote for Johnson fully oppose Trump and fully oppose Clinton.
Anyway, I don't care whether any of the Bushes endorses Johnson, but I'm glad to know that they're not supporting Trump. Fully and completely.
He's talking mathematically, and he's right, in terms of net margin
