Part of the reason is that people who consider Trump and Clinton on equal terms on these things tend to favor Trump by a large — and even increasing — margin.
While 57 percent of registered voters view Clinton as being qualified to serve as president, just 43 percent say the same of Trump.
But 1 in 5 registered voters view Trump and Clinton on equal terms when it comes to whether they are qualified to serve as president — either because both are qualified, or because neither is — and among this group, Trump leads Clinton by 35 points, 48 percent to just 13 percent.
Among this group, in fact, Libertarian Gary Johnson actually has a statistically insignificant edge on Clinton. He takes 16 percent of these voters.