Yes, and strategically and practically speaking, the next battlefield coming up is the midterm congressional elections.
Joe's numbers will probably always be up there a bit because favorability and likeability all get mushed together in some of those polls, and Joe will always be the hapless, crazy uncle who shows up for Thanksgiving. You roll your eyes but there is no reason to dislike him so that gets him a 40% base to start from.
The thing that is scary for dems though is that Joe will never rise to Obama's Baby Jesus rating and status- yet dems got absolutely slaughtered in his first midterms. There may be other reasons why dems can hold up at midterms but it will not be the force of Joe's personality and performance. Oh, and did I mention that the dem lead over pubs in the house is razor thing compared to Obama's just going into the midterms.
Longwinded way of saying Joe's numbers can whip all over the place and lefties here and in the media will try to tell that means a lot. Okay, whatever. Maybe if just feeling good about Joe is your definition of "a lot." But if "a lot" means things like holding on to the House, then I would start looking for "a lot" of something other than Joe to make your case if I were a dem.
I could be wrong. Joe's ratings could be higher than Obama's and at mid-terms he will be out in Pocatello, Idaho surfing on the crowd and getting out the vote. If the recent election is any indicator though, the less they see of Joe the better for dem numbers.