He isn’t going to quit anytime soon. He is going to run on the obstruction angle now, and that may take years just waiting for President Trump or his administration to make just one small misstep.
The irony in that is that DJT could declassify enough material to let the air out of the Mueller ballon, and could have done so a year ago. It is far from obvious that Mr. Trump actually wants the Mueller witch hunt to end - apparently he actually likes complaining about it.