Oh please. Teddy Kennedy used it against Romney in the campaign for Senator years ago. It is part of why he beat Romney. Primary voters have a right to vett the candidates. Better to know about it now, than to be surprised with it after he becomes the nominee.
If he can't explain it well enough to get Pubbies to vote for him, then he has no chance of explaining it well enough in the general to beat Obama.
I was actually being sarcastic there. ;-)