Former President Clinton frequently blows up in anger while campaigning for his wife.
The interesting question is: why.
Does he feel he and his wife are somehow owed the office of the presidency?
Does it enrage him that other Democrats dare to challenge the Clintons, and criticize them?
Fundamental: no one is owed the office of the presidency, and it's very dangerous for anyone to believe that he/she are. Power corrupts.
UPDATE: And there's also this quote from the former president, from an article in today's Washington Post:
"The Republicans were so mean to me when I was president that I was poorer when I left than when I got there."
You poor victim. How much money did you make on your autobiography, again? How much money were you being paid per speech in the last seven years? You're pathetic, Mr. Clinton.