Riots provoke a conservative "law and order" backlash, and Obama doesn't want that anymore than Johnson and Humphrey did.
I guess the fantasy is that a president of the other party always wants to suspend the elections and declare martial law, but none of them ever do.
Here's the thing: politicians like to be in the news; they like being famous; they like wielding some power; but they don't really want to hold office and power forever, if it means forever expecting revolution or assassination.
Most of them have adapted to the fact that they will be voted out or forced to leave by term limits, but even if they haven't, they get sick of the headaches and worries and don't want to rule permanently.
Hitler.
Stalin.
Mao.
Mussolini.
Pol Pot.
Mugabe.
Idi Amin.
Some do. Don't think for a second that Barry the Boob wouldn't do it.