Reaching anew for peace, President Obama and Russian President Dmitry Medvedev on Thursday signed a treaty to shrink their nations' nuclear arsenals, the biggest such pact between the former Cold War foes in a generation.
Tenaciously negotiated by even the leaders themselves, the treaty commits their nations to slash the number of strategic nuclear warheads by one-third and more than halve the number of missiles, submarines and bombers carrying them.
In a lavish chamber within the Czech capital's presidential castle complex, the two presidents put their names to history.
"Today is an important milestone for nuclear security and nonproliferation, and for U.S.-Russia relations," Mr. Obama said. Medvedev hailed the signing as a historic event that would launch a new chapter of cooperation between the countries.
Said the Russian president: "The entire world community has won."
The treaty would cut the strategic nuclear arsenals of the United States and Russia by about a third, down to about 1,500 warheads apiece, CBS News Chief White House Correspondent Chip Reid reports from Prague. That's still a lot - enough to destroy both countries - but the president says it's an important step along the road to a world without nuclear weapons, Reid reports.
Mr. Obama admits getting there will take generations, but he said you've got to start with the U.S. and Russia because they have more than 90 percent of the world's nuclear weapons, Reid reports.
"The result we have obtained is good," Medvedev said.
Negotiations between the U.S. and Russia got bogged down in disputes, including Russia's objection to U.S. missile defense plans for Europe. The Kremlin is still concerned about the plan but sought to tamp down talk it would withdraw from the new treaty if there is a buildup in the missile defense system. Russia codified its option to withdraw in a statement in connection with the treaty.
Mr. Obama said the treaty itself built trust that would help in solving any differences on the issue. Responded Medvedev: "I am an optimist as well as my American colleague. I believe that we will be able to reach a compromise."
The treaty must be now be ratified by Russia's parliament and by the U.S. Senate, where the White House lobbying effort is under way.
"I feel confident that we are going to be able to get it ratified," Mr. Obama said.
Senior White House officials say they're hopeful of ratification in the Senate later this year, Reid reports. The officials say the 67 votes needed for ratification will likely be garnered along party lines.
"It is clearly a legacy issue for the Obama administration," says CBS News foreign affairs analyst Pamela Falk, "but the administration has built in wiggle room on development of weapons to satisfy some conservative critics and, although it will take some time to pass, it is clear that the treaty improves U.S.-Russian relations and will have strong backing from the president himself."
More on Obama's nuclear strategy:
Read the Treaty
China Leader to Attend U.S. Nuke Summit
Nuclear Posture Review Report(PDF)
Inside the hall, the anticipated moment came as the two presidents picked up their pens, glanced at each other and grinned as they signed several documents, with aides transferring the papers back and forth so all would have both signatures. When it was done, the leaders seemed momentarily at a loss, with Medvedev flashing a smile and a shrug before they stood to shake hands.
Mr. Obama said the treaty sets a foundation for further cuts in nuclear arms.
And he pledged more conversation with Medvedev about missile defense, which remains a sticky issue between the countries as the U.S. moves ahead with plans it calls no threat to Russia. Mr. Obama said the missile defense system envisioned is not aimed at changing the "strategic balance" with Russia but rather as a way to counter launches from other countries.
Medvedev said he was optimistic about reaching a compromise on the matter.
Beyond deeply reducing nuclear arsenals, the U.S. sees "New START" as a key part of efforts to "reset" ties with Russia, which had become badly strained under the Bush administration and engage Moscow more in dealing with global challenges. Among these is Iran's defiance of U.N. Security Council demands that it curb its nuclear program to ease fears it seeks to make nuclear arms.
Obama called the spread of nuclear weapons to more states an "unacceptable risk" to global security that could raise the specter of arms races from the Middle East to East Asia.
Looming over the celebration was Iran, which in the face of international pressures continues to assert that its uranium enrichment program is for peaceful purposes, not for weapons as suspected. Six powers - the U.S., Russia, Britain, France, Germany and now China - are in talks in New York about a fourth set of United Nations sanctions to pressure Iran into compliance.
"We cannot turn a blind eye to this," Medvedev said in a show of solidarity. But he said he was frank with Obama about how far Russia was willing to go, favoring only what he called "smart" sanctions that might have hope of changing behavior.
Obama, Medvedev Pledge to Pursue Iran Sanctions
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In terms of ratification in the Senate, Obama emphasized the history of Senate bipartisanship on arms control matters. But that could be wishful thinking this year.
The GOP could well see an irresistible opening to criticize the broader security policies of Obama and his Democratic allies. Even if Republicans don't reject the treaty, they could seek to postpone its ratification to deny Obama a victory ahead of the November midterm elections.
One potential GOP backer, Richard Lugar of Indiana, a moderate Republican steeped in nonproliferation issues and the top GOP lawmaker on the Senate Foreign Relations Committee, has been curiously quiet.
But Republicans are expected to eventually swing behind the treaty if Obama can promise it won't undercut the nation's ability to set up missile defenses to protect against an attack from Iran or North Korea. Senate Republican leader Mitch McConnell said the GOP also wants assurances that the agreement will preserve the nuclear triad, a reference to the three tiers of the nation's nuclear defense.
Senate Majority Leader Harry Reid, D-Nev., issued a statement welcoming the treaty and warning Republicans not to "play politics with something as important as this to our national security." He said he was confident the agreement would be ratified.