One year ago, on April 5, 2009, Barack Obama delivered what may have been the most important speech of his young presidency.

Speaking to a crowd of 20,000 in Prague, he declared:

"One nuclear weapon exploded in one city — be it New York or Moscow, Islamabad or Mumbai, Tokyo or Tel Aviv, Paris or Prague — could kill hundreds of thousands of people. And no matter where it happens, there is no end to what the consequences might be — for our global safety, our security, our society, our economy, to our ultimate survival."

Obama said exactly the right thing.

Now, he must do exactly the right thing.

The president is taking some important steps this month. On Thursday, he will return to Prague to sign a "New START" treaty — named for the Strategic Arms Reduction Treaties of the early 1990s — that promises a meaningful reduction in deployed long-range nuclear warheads. The treaty is significant, both on practical and symbolic grounds.

The same goes for the summit on arms safeguards that Obama will host on April 12 and 13.

But where the president needs to step up is at the Nuclear Non-Proliferation Treaty Review Conference, which opens at the United Nations in May.

It will be the president’s opportunity to follow through on the pledge he made in Prague to position the United States as a global leader not merely for nuclear disarmament but the abolition of the doomsday weapons that threat "our global safety, our security, our society, our economy, to our ultimate survival."

Peace Action, the nation’s largest grassroots peace and disarmament network, is asking Americans to email the president with a plea that he act on the promise made in Prague. It reads:

Dear President Obama,

We wholeheartedly applaud you for declaring in Prague, “I state clearly and with conviction America’s commitment to seek the peace and security of a world without nuclear weapons.” We commend you for your courageous and historic recognition that “as the only nuclear power to have used a nuclear weapon, the United States has a moral responsibility to act.” We call on you to make good on that commitment and fulfill that responsibility by announcing at the 2010 Nuclear Non-Proliferation Treaty Review Conference your initiation of good faith multilateral negotiations on an international agreement to abolish nuclear weapons, within our lifetimes! Yes we can!!

In addition to sending the email, Peace Action is asking activists to download paper petitions and gather signatures as part of a push to add 100,000 signatures to an international petition seeking abolition of nuclear weapons.

The president talked the talk in April of last year.

Now, he needs to walk the walk in April of this year.

This no time for caution or political positioning.

Obama must lead without apology or compromise.

He must recognize anew the truth of the words he spoke in Prague on April 5, 2009, when he said: "Some argue that the spread of these weapons cannot be checked, that we are destined to live in a world where more nations and more people possess the ultimate tools of destruction. This fatalism is a deadly adversary, for if we believe that the spread of nuclear weapons is inevitable, then we are admitting to ourselves that the use of nuclear weapons is inevitable."