This article was originally published in the Wall Street Journal

When Barack Obama becomes America’s 44th president on Jan. 20, he should embrace the vision of a predecessor who declared: “We seek the total elimination one day of nuclear weapons from the face of the Earth.”

That president was Ronald Reagan, and he expressed this ambitious vision in his second inaugural address on Jan. 21, 1985. It was a remarkable statement from a president who had deployed tactical nuclear missiles in Europe to counter the Soviet Union’s fearsome SS-20 missile fleet.

President Reagan knew the grave threat nuclear weapons pose to humanity. He never achieved his goal, but President Obama should pick up where he left off.

The Cold War is over, but there remain thousands of nuclear missiles in the world’s arsenals — most maintained by the U.S. and Russia. Most are targeted at cities and are far more powerful than the bombs that destroyed Hiroshima and Nagasaki.

Today, the threat is ever more complex. As more nations pursue nuclear ambitions, the world becomes less secure, with growing odds of terrorists obtaining a nuclear weapon.

The nuclear aspirations of North Korea and Iran threaten a “cascade” of nuclear proliferation, according to a bipartisan panel led by former U.S. Defense Secretaries William J. Perry and James R. Schlesinger.

Another bipartisan panel has warned that the world can expect a nuclear or biological terror attack by 2013 — unless urgent action is taken.

Nuclear weapons pose grave dangers to all nations. Seeking new weapons and maintaining massive arsenals makes no sense. It is vital that we seek a world free of nuclear weapons. The United States should lead the way, and a President Obama should challenge Russian President Dmitry Medvedev to join us.

Many of the world’s leading statesmen favor such an effort. They include former Soviet leader Mikhail Gorbachev, former Defense Secretary Perry, former Secretaries of State Henry Kissinger and George Shultz, and former Senate Armed Services Committee Chairman Sam Nunn.

Unfortunately, for eight years the Bush administration moved in another direction, pushing aggressive policies and new weapons programs, threatening to reopen the nuclear door and spark the very proliferation we seek to prevent.

President Bush made it the policy of the United States to contemplate first use of nuclear weapons in response to chemical or biological attack — even against nonnuclear states.

He changed the “strategic triad” — which put nuclear weapons in a special category by themselves — by lumping them with conventional weapons in the same package of battlefield capabilities. This blurred the distinction between the two, making nuclear weapons easier to use.

And he advocated new types of weapons that could be used in a variety of circumstances against a range of targets, advancing the notion that nuclear weapons have utility beyond deterrence.

Mr. Bush then sought funding for new weapons programs, including:

– A 100-kiloton “bunker buster” that scientists say would not destroy enemy bunkers as advertised, but would have spewed enough radiation to kill one million people.

– The Advanced Concepts Initiative, including developing a low-yield nuclear weapon for tactical battlefield use.

– The Modern Pit Facility, a factory that could produce up to 450 plutonium triggers a year — even though scientists say America’s nuclear triggers will be good for years.

– Pushing to reduce time-to-test readiness at the Nevada Test Site in half — to 18 months — signaling intent to resume testing, which would have broken a test moratorium in place since 1992.

– A new nuclear warhead, called the Reliable Replacement Warhead, which could spark a new global arms race.

I opposed these programs, and Congress slashed or eliminated funding for them.

But President Bush had sent dangerous signals world-wide. Allies could conclude if the United States sought new nuclear weapons, they should too. Adversaries could conclude acquiring nuclear weapons would be insurance against pre-emptive U.S. attack.

Here’s how President-elect Obama can change course. By law he must set forth his views on nuclear weapons in U.S. national security strategy, in his Nuclear Posture Review, by 2010. In it, he should commit the U.S. to working with Russia to lower each nation’s arsenal of deployed nuclear warheads below the 1,700-2,200 the Moscow Treaty already calls for by 2013.

It would be a strong step toward reducing our bloated arsenals, and signal the world that we have changed course.

I was 12 when atomic bombs flattened Hiroshima and Nagasaki, killing more than 200,000 people. The horrific images that went around the world have stayed with me all my life.

Today, there are enough nuclear weapons to destroy the world hundreds of times. And we now face the chilling prospect of nuclear terrorism.

The bottom line: We must recognize nuclear weapons for what they are — not a deterrent, but a grave and gathering threat to humanity. As president, Barack Obama should dedicate himself to their world-wide elimination.

Dianne Feinstein is a Democratic Senator from California.