Amazingly, I have one.
A time-travel adventure series, a la Quantum Leap, but a team. They have to go back in time and "fix" events to make them align with the current universe, which has been determined to difinitively be in the class of best of all possible universes.
The twist: Every event they have to "fix" are tragedies and horrors. They have to blow up the Hindenberg. They have to kill Lincoln. They have to save Hitler's life. They have to initiate the abuse at the Iraqi prisons.
Eventually, one of the team starts to wonder about the morality of sacrificing the past for the benefit of the future, and begins to sabotage missions. Another narrative thread begins when the viewers start to see what the botched missions change.
This aligns with something I was going to suggest:
A man goes back in time and kills Hitler, As a result command is taken over by one of his more competant underlings. As a result the german side hangs on long enouh to complete their nuclear weapons program and the earh is devestated by 2 way nuclear war