It will be interesting to see if this changes how Bernie approaches the debate tonight and whether his campaign now becomes willing to more proactively "take on" Hillary.

Sanders staffer shouldn't have snooped around the database, but the reaction and punishment by the DNC was too harsh.  And I think that finally exposed the nerve that has been bugging the Sanders campaign all along, which is the fact the DNC really wanted this to be a coronation for Hillary and not have a repeat of 2008 when an unknown came out and beat her.

Maybe Sanders will be upset enough to do his own 3rd party candidacy.

What choice did the Sanders campaign have?  Remember that Bernie was elected and remained an 'independent' until he decided to run for president.  The mucky-mucks within the DNC machinery ( especially Debbie Wasserman-Shultz) were probably bent on throwing Clinton out there from Day One.  Sanders and his anti-corporate, progressive stance on issues coupled with his growing popularity got their knickers knotted and they don't know what to do about it.  

With the race increasingly turning on security and terrorism, Bernie's moment is gone.

Perhaps, time will tell.  Sanders tends to link things like terrorism and security to such things as the ever-widening wage gap, unemployment, etc., believing that terrorist groups move in when people feel dissatisfied, angry, pessimistic, caged in, or hopeless about their future.  Sanders feels if a person senses alienation from the rest of society or unable to alter their position in life, they become a pliable target for a radical organization like ISIS or any number of similar crime families.