It's instructive to see where the race was in the Spring of 2012 - and well, exactly where it is now.
Quinnipiac 4/3-4/9 2012: Obama +9 49/40
Quinnipiac 5/9-5/14 2012: Obama +10 49/39
NJ is safe Clinton.
I question your assumption that 2012 polls are "instructive" in 2016. In 2012, the Democratic candidate was an incumbent, which significantly makes that race different from this race; and you must remember that Hurricane Sandy likely caused Obama's ultimate margin of victory over Romney in New Jersey.
Bush came within 5% of New Jersey in a tight race. Trump, who has ties to the Northeast, could feasibly get closer if he runs a great campaign (or Hillary runs a bad campaign).
You can "question" my assumption but all I did was point out that polls at the same time in 2012 showed the race as high single digits or low double digits. The same as it is now - Trump is not winning NJ.