Silver's predictions of the election outcome took much of the shine off the statistician-pollster-guru, and no amount of statistical spin ("we were expressing our confidence that the unpredictable wouldn't happen, but we left open the possibility of the unpredictable!") can restore it to its former glory, but this Fivethirtyeight explainer on the polls that show a huge variance in Trump's approval and disapproval ratings is the kind of detailed analysis that is mostly light, with little heat.
The first thing to note is that while automated robo-call polls -- which are more favorable to Trump -- allow people to express their views on Trump without risking social disapproval from the human on the other end of the phone (the "shy Trump supporter" phenomenon), they also only survey landlines, which means they exclude fifty percent of American voters.
The second thing to note is that the historic presidential popularity polls have surveyed all US adults, and Trump's approval ratings are worst in this cohort. However, when you narrow that down to "likely voters," Trump's rating climbs a lot. So: compare Trump's popularity against other presidents with the "all US adults" polls, but think about his re-election possibilities by paying attention to "likely voters." But note: "likely voter" is a slippery concept -- opponents who are enraged by Trump for two years may be more likely to vote, Trump supporters who are disillusioned with him might not vote at all. Or, contrariwise: people who spend two years being enraged by Trump may be so demoralized that they stay home; while people who supported Trump may go back to the polls in 2018 to double down on him, rather than face the cognitive dissonance of having made such a dumb mistake.
The final thing to note is that Trump's disapproval rating is unprecedentedly high for a newly elected president, but not for a president overall. Obama's disapproval rating was at Trumpian levels through most of his tenure. So stop counting chickens and high-fiving. A lot of people like what Trump is doing. Why they like it is up for grabs: maybe they're racist assholes, maybe they feel no stake in the existing order and want to see it burned down, maybe they are dumb enough to believe Trump's spin. Maybe none of the above, or a combination.
Trump has a fairly poor 43 percent approval rating — and a 51 percent disapproval rating — among polls of all American adults, but he improves to a 47 percent approval rating and a 49 percent disapproval rating among polls that survey registered voters or the narrower group of likely voters. That’s a reasonably big difference. So which polls should you use?
Traditionally, approval rating polls are conducted among all adults, so those are probably better for making historical comparisons. And there’s something to be said for inclusivity if your goal is to assess the extent to which Trump has a mandate with the public. He is, after all, the president of all Americans and not just those who are registered to vote or who do so regularly.
But for forward-looking, predictive purposes — to assess the effect that Trump will have on the midterms, for instance — the voter-based polls are probably more useful.
While there can be good reasons for using polls of voters as opposed to those of all adults, however, I’d be wary of making too much about the difference between registered-voter and likely-voter polls. At this early stage, it’s hard to predict what the likely voter electorate will look like in 2018. Midterm voters are typically older and whiter than registered voters overall, which should help Republicans. But they’re also better-educated, which should help Democrats. Furthermore, the “enthusiasm gap” can vary quite a bit from election to election, although it usually favors the opposition party in the midterms (i.e., Democrats in 2018).
Why Polls Differ On Trump’s Popularity