President Barack Obama headed to Prague Wednesday night to sign an arms treaty with Russian President Dmitri Medvedev. Next week, the White House will host a major nuclear-weapons summit that will include more than 30 heads of state. Prague was the site of Obama’s speech last year in which he called for a nuclear-free globe. It’s a huge goal that likely won’t be met in this administration, but the president aims to show the world he’s serious. Newsweek offers him a to-do list to further those goals, including making good on a promise to renew relations with Russia, tell countries with ambitious terrorists that they’ll be held accountable, pressure “outlier” states, and be sincere about shrinking weapons stockpiles.