The US and Russia have now pledged that they will carry out perhaps the deepest warhead cuts of the atomic age. But pledged is not the same as done, and details left unresolved after Russian President Vladimir Putin's White House visit might loom large in the months and years to come.
Just look at the tough messages Putin slipped into his generally warm remarks at his joint press conference with President George Bush.
We like the idea of massive weapons reductions, said Putin. But we like written treaties, too. In particular, we still like the 1972 Anti-Ballistic Missile Treaty - the very pact that for months President Bush has been calling a dead letter.
The bottom line: The US sees the nuclear future as paperless, with two friendly nations no longer needing treaties to bind them. Russia still wants the assurance of an overall nuclear-treaty regime. Whatever the agreement on weapon numbers, the disagreement on this important point needs to be resolved if the relationship between the two nations is to match the rhetoric of their leaders.
"This [warhead] agreement [raises] a host of questions - if you can call it an agreement," says Christopher Paine, a research associate in nuclear issues at the Natural Resources Defense Council in Washington.
It's possible that the final word on Putin's near-term intentions has not been written. Perhaps the two presidents will now announce a further dramatic breakthrough on missile defenses and related nuclear issues at the dramatic locale of Bush's ranch in Crawford, Texas.
Furthermore, the nuclear accomplishments of Putin's US visit are already significant.
The two sides pledged to reduce their respective nuclear stockpiles by approximately two-thirds over the next decade. For the US, that would mean a range of 1,700 to 2,200 warheads, said Bush.
That's similar to the range of warhead levels discussed by President Bill Clinton and Russia President Boris Yeltsin in 1997 talks about a notional Strategic Arms Reduction Treaty (START) III. It goes well beyond the 3,000 to 3,500 limits set by the START II pact, which was signed by President George H. W. Bush and Mr. Yeltsin in 1993.
Indeed, the lower end of Bush's announced range is well below the warhead levels that Adm. Richard Mies, head of US Strategic Command, said during a congressional appearance earlier this year were necessary to ensure US security.
START II has never gone into effect, since political difficulties in both Russia and the US clogged up the legislative ratification process. And that's the beauty part of the unilateral cuts envisioned by Bush, say US officials. They won't get derailed by peripheral issues. They'll be clean and simple. No large negotiating delegations will live in plush neutral cities like Geneva and take months arguing over minute points of Subsection C, Protocol 14.
"Current levels of our nuclear forces do not reflect today's strategic realities," concluded Bush.
But Tuesday's reduction pledges left a number of important issues unaddressed, say some nuclear experts. Among them may be the actual warhead number US officials envision for the future.
That's because Bush used the phrase "operationally deployed" weapons. Several hundred warheads are being refurbished or stored at any one time, and it's not clear whether they will be counted as part of the stockpile, as they have been in the past. Furthermore, it holds out the prospect that large numbers of warheads could simply be unbolted from delivery vehicles and stored somewhere, awaiting a day when rising tensions might necessitate their redeployment.
"Will those warheads simply go into a strategic reserve? Look out for fuzzy math here," says Daryl Kimball, executive director of the Arms Control Association in Washington.
Putin may be of similar mind. He did propose reductions in Russia's arsenal that would proportionally match the US cuts. But he also appeared to insist on them being accompanied by written agreements that would address the verification of what had happened, and perhaps ensure it could never be undone.
"Today, the world is far from having international relations based on trust," said Putin in remarks at the Russian Embassy on Tuesday evening. "That is why it's so important today to rely on the existing foundation of treaties and agreements in the arms-control ... area."
It remains to be seen how important this objection could become. Would Russia really hold on to some warheads if the US refuses to enter into some form of written pact on the subject? Would the US risk that happening?
While US and Russia relations now appear as warm as at any time since World War II, it's only a nascent friendship, say some US experts. There are many ways it could sour. Why not hammer out a quick weapons-cut pact?
"The president should be locking in historically low nuclear-weapons rates," says Joseph Cirincione, a senior analyst at the Carnegie Endowment for International Peace in Washington. "Instead, he's opting for a flexible warhead 'mortgage' that could go up or down."
But the issue of missile defenses would surely complicate any attempt at getting warhead reductions in writing. US officials appear no closer to obtaining Russian agreement with the Bush-administration view that the ABM Treaty is an impediment to the necessary self-defense of an antimissile shield.
Bush seemed to acknowledge as much when he said that "we will continue dialogue and discussions about the ABM Treaty so that we may be able to develop a new strategic framework that enables both of us to meet the threats of the 21st century."