Also worth noting here that despite Christie losing ground in the GE, he's still doing better than any of his Republican rivals against Clinton. Have we seen any recent polls in which Christie was not the strongest Republican in the GE matchups?
There are none. There is one poll from one year ago that had Clinton beating Christie by 5 and beating Bush and Ryan by 6. That's the closest thing you will find. He is by far, today, the most electable Republican candidate. Paul, Ryan and Bush seem to be the next most electable at this point.
This is an average Clinton's lead of all the polls I took from Wikipedia.
Christie - 4.4
Bush - 9.8
Ryan - 10.3
Paul - 10.3
Rubio - 11
Cruz - 16.3
Perry - 18