The chart above is from a recent YouGov Poll -- done between July 15th and 17th of a random national sample of 1,300 adults, and has a margin of error of 4.3 points.
I thought the survey was interesting because it didn't ask who the respondents support for president, but instead it asked who they could consider voting for or never vote for. Make of it what you will.
Note that only one presidential candidate is not upside-down in these numbers. Hillary Clinton is the only candidate to have more people say they could vote for her than say they would not vote for her -- and the only candidate to have at least 50% saying they could vote for her.
