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President Obama has a once-in-a-generation opportunity over the next few months to help make the world a dramatically safer place. It's not by negotiating an arms deal with Russia, or strengthening the nuclear Non-Proliferation Treaty, or by making that elusive climate-change deal with the Chinese, worthy though those initiatives may be. It is by helping the Iranian people achieve a new form of government. Given the role that the Islamic theocracy in Tehran has played in leading and sponsoring anti-democratic, anti-liberal and anti-Western fanaticism for the past three decades, the toppling or even substantial reform of that regime would be second only to the collapse of the Soviet Union in its ideological and geopolitical ramifications.