Conservatives on Twitter are buzzing about this as a sign that Trumpmania may be overblown. If Trump fans aren’t likely to actually turn out for him once we start counting votes, who cares what his polls say? (Maybe not coincidentally, Rasmussen’s post-debate poll of likely Republican voters was the worst one for Trump this week.) I was surprised at the numbers at first, thinking Trump’s fan base is probably mostly composed of older voters. Older voters tend to skew right, after all, and older voters would be more familiar with him from his decades of fame. And older voters...