Most polls I've seen have had him around 45% approval and 52% disapproval. (see link).

And for primary results, Obama had 89% of the democratic vote in 2012 , George W Bush had 98% in 2004, Clinton had 89% in 1996. This is more about if there are any serious challengers, in my opinion.

Bellwethers change over time, as well. Arkansas, Tennessee, Kentucky, Montana and Colorado have all been considered bellwethers up until the last decade or two.

Finally, the number of votes exceeding the number of registered voters usually cite the number of registered voters a few days before the election (so that they have time to push a number out). Quite a few states have same day voter registration, and on election day the counties have other things that take priority over publishing statistics.