This is what I was getting at. What we want to know is which voters are most likely to turn out. To be a bit reductionist, what's the difference between likely voters and registered voters, or likely voters and all eligible adults? That's a good measure of the "enthusiasm gap".
The Upshot/Siena polls publish this RV/LV comparison. Fox News, CNN, Marist, Monmouth also do so most of the time. On average, we show the GOP doing about 0.4 points better on LV polls than RV ones, which is obviously a small gap (although it was like 0.0 a few weeks ago).
One thing that *may* be going on re: Kavanaugh is that the GOP base voters are becoming more enthusiastic, but high-turnout-propensity swing voters (e.g. wealthy suburbanites) are turned off by him. So there are effects working in opposite directions.
