As for Mr Obama, he has a chance to restore America’s moral leadership. That is not something he should do by scouring the world in search of new monsters to slay. Nor, though, can a war-weary America turn its back on people threatened by ethnic cleansing or genocide. Since 2005 the UN has accepted a responsibility to protect people in such cases, so this is not a burden for America alone. But since the UN has no army, and no other countries have the military resources America boasts, there may be times when only the superpower can move soldiers swiftly where they are needed.
Should that call come, Mr Obama will need the courage to respond, notwithstanding Americans’ fatigue. In extremis, if the danger is great and veto-wielding members of the Security Council block the way, he and others might have to act without the Security Council’s blessing, as NATO did in Kosovo. Far better would be an early effort by Mr Obama to reach agreement on the rules to apply and forces to earmark so that the UN can actually exercise its collective responsibility to protect. That will be hard, but Mr Bush was actively hostile to such work. How fitting if the next president made possible a genuinely global response to the next Rwanda, Congo or Darfur.