If 45% of adults approve of Trump, how many will vote for him?

Polls don’t provide a clear answer

Adam emails:

The NBC poll has Democrats up vs Trump but Trump approval at 47-50. What is up with that? Is this a polling issue or something else? He would be underperforming his approval by 1 to 3 points. I tweeted you about this but there are a lot of comments.

What he points out is super interesting and worth talking about. In the most recent NBC News/Wall Street Journal poll, Trump’s job approval rating is 47% and his disapproval is 50% (-3). On average versus his Democratic opponents, the president is underwater by six percentage points (44 v 50 percent). That means he’s underperforming his approval ratings by 3 percentage points.

This is indeed a departure from what I’ve observed in other data. It’s a bit hard to know what’s causing the pattern or what to make of it. In YouGov’s polling, for example, Trump has been hovering around a 5 percentage point deficit in the generic presidential ballot over the past month. All the while he has been about 10 percentage points underwater on n…