The first major challenge of a front runner: squash petty distractions

Clinton had his mistresses, smoking pot, and avoiding Vietnam.
Gore had a poorly attributable quote, "I invented the internet."
Kerry had, "I voted for before I voted against it."
Obama had Reverend Wright and Bill Ayers.
Hillary had emails.

Two people on this list successfully squashed their petty distractions during the campaign and went on to victory. The other three did not.

When a campaign allows for a petty distraction to consume your message, you are starting to lose. Bernie's Castro quote may be the pettiest distraction of them all, but it's starting to consume his entire message like widlfire. And, the candidate himself is giving oxygen to these flames by making an intellectual argument against an emotional one.

What can be won by arguing this point with people who have a negative, emotional reaction to Castro. This is a campaign for the presidency, not a class lecture on world history.

Squash it and move on.