Barack Obama’s decision not to intervene militarily in Syria led to the deaths of hundreds of thousands of Syrians and the exodus of millions more. You could argue–and I would–that the alternative was even worse, based on the outcome in Iraq, the Russian interest in the status quo, and the lack of a unified opposition to Assad. You can’t reasonably deny, however, that refusing to intervene came with heavy costs.
Warren and Sanders are even more hostile to the notion of military interventions than Obama was. They should be asked about Syria during the debates, because if you’re not willing to be the world’s policeman, you have to be openly prepared to tolerate a lot of damage that will be done by some pretty thuggish characters. That’s the tradeoff. It can’t be avoided.