There are 7 directory authorities in Tor, if they don't function then the tor network is dead. So that is just seven people you would need to abduct and torture (to take over the tor network) or 7 drone strikes to kill all tor traffic.
I am unsure but I think this is not the case for i2p.
EDIT:
So that might be a reason for NSA to support Tor over i2p.
There are 7 directory authorities in Tor, if they don't function then the tor network is dead. So that is just seven people you would need to abduct and torture (to take over the tor network) or 7 drone strikes to kill all tor traffic. I am unsure but I think this is not the case for i2p.
EDIT: So that might be a reason for NSA to support Tor over i2p.