In the early going, there just isn't a lot of good polling data out there to understand the playing field. CNN rates 11 Senate races as either competitive (i.e. Most of these seats have very little non-partisan polling for them. Now in some races there have been a ton of non-partisan polls such as Florida (12) or Missouri (7), but in other races there have been zero. While a number of key Senate races haven't been polled at all this cycle, every single competitive race had at least one poll taken in it by this point in the last midterm cycle in 2014.

Source: CNN May 20, 2018 17:03 UTC