The U.S.-Russian arms treaty may not be big news, but it's good news.

Four things should be noted about the new strategic arms-reduction treaty announced Friday by President Barack Obama and Russian President Dmitri Medvedev.

First, it doesn't reduce strategic arms much at all. Second, it might improve U.S.-Russian relations on a host of other issues. Third, though Republicans in the Senate will be desperate to block a nuclear-arms treaty that adds to Obama's political luster, they will have a hard time mustering any objections to this treaty on substantive grounds. Fourth, though Obama and Medvedev will sign it in Prague next month, just two weeks before the 40-nation conference on nuclear proliferation, the treaty will probably have no impact on other nations' desires to build their own nuclear bombs.

In sum, the new treaty is a good thing—for Obama, politically, a very good thing. But nobody should make a big fuss over it one way or the other.

First, what does this treaty do?

It forces each side to reduce the number of its "strategic delivery vehicles"—its long-range missiles (land-based intercontinental ballistic missiles, or ICBMs, and submarine-launched ballistic missiles, or SLBMs) and its heavy bombers—to no more than 800. Of those 800 vehicles, no more than 700 can be "deployed"—that is, actually loaded with nuclear warheads or bombs. (In other words, about 100 can be in storage or loaded with non-nuclear weapons.) It also forces each side to reduce the number of nuclear warheads and bombs loaded on those missiles and bombers to 1,550.

At first glance, this is pretty big news. The 1991 START agreement, which expired in December, let each side have 2,200 warheads and bombs on 1,600 missiles and bombers. By that measure, this new treaty slashes the limits on nuclear warheads and bombs by 30 percent—and the limits on missiles and bombers by half.

However, a closer look proves a bit less dramatic. Over the years, both sides have cut their nuclear arsenals on their own initiative. The United States now has about 850 strategic delivery vehicles (very close to the new treaty's limit), and Russia has about 600 (below that limit). The U.S. has 2,252 bombs and warheads, while Russia has about 2,787—closer to, or a little above, the '91 treaty's limits. So the new treaty will force some cuts on both sides—but not as deeply as these numbers suggest.

According to the treaty's counting rules, if, say, a U.S. Minuteman 3 ICBM has three warheads and a Russian SS-19 ICBM has six warheads, then they will be counted as having three and six warheads, respectively. However, all bombers will be counted as if they were carrying just one nuclear bomb apiece, even though they can (and almost certainly do) carry several. This counting rule, which was written into the '91 treaty too, makes sense for practical reasons: Bombs can be loaded on and off an airplane at a moment's notice; a strategic bomber can carry a couple of nuclear bombs one day, a dozen the next.

As a result of this counting rule, both sides can meet the treaty's limits without really cutting that many weapons.

Here is a good unclassified estimate of both sides' current arsenals:

United States
ICBMs: 450 missiles, 550 warheads
SLBMs: 288 missiles, 1,152 warheads
Bombers: 113 planes, 550 bombs

Russia
ICBMs: 383 missiles, 1,355 warheads
SLBMs: 160 missiles, 576 warheads
Bombers: 77 planes, 856 bombs

In total,  the United States has 2,252 strategic nuclear bombs and warheads, while Russia has 2,787—suggesting that the treaty would force the U.S. to cut 702 and Russia to cut 1,237. However, if each bomber is counted as having just one nuke inside, this means the United States has to count just 113 of those bombs, not 550, and Russia can get by counting just 77, not 856. Therefore, the United States is counted as having a total of 1,815 warheads and bombs, while Russia is counted as having 2,008—meaning they have to cut their present arsenals by just 265 and 458, respectively.

Finally, the treaty does nothing to reduce each side's stockpile of short-range "tactical" nuclear weapons. The precise numbers of these tac nukes are not exactly known (one reason no treaty, including this one, has attempted to limit them), but estimates put them at about 500 for the United States and about 2,000 for Russia.

In short, the new treaty does something to reduce nuclear weapons. But it doesn't cause much of a strain.

So, on to the second point: The treaty's effect on other issues in Russian-American relations. U.S. officials say that the good cheer engendered by the treaty will build mutual trust, which could lead to more cooperation on matters that really count these days: terrorism, nuclear proliferation (including joint efforts to stop Iran's uranium-enrichment program), climate change, and so forth.

During the Cold War, nuclear arms-control talks were a surrogate for diplomacy. They gave U.S. and Soviet diplomats something to talk about—let them get to know each other, scope out intentions, reduce distrust—at a time when political disagreements made it impossible to talk about anything else.

After the Cold War ended, the two countries could suddenly talk about lots of issues. The icy exchanges between George W. Bush and Vladimir Putin pumped a bit of frost back into the air. A renewed START accord will help "push the restart button." That's the (explicitly stated) hope, anyway. We'll see. One thing's for sure: If the treaty had collapsed, so would have the prospects for cooperation in other areas.

The third point: Will the U.S. Senate ratify this treaty? It takes 67 senators, not just 60, to pass an international treaty into law. This means eight Republicans must go along with it—more if the vote is delayed until after November and the Democrats lose a few seats. (Such a delay wouldn't be unusual in the annals of arms control.)

Still, Obama's opposition faces a major problem: It would be a huge stretch, even by contemporary Republican standards, to find anything wrong with this treaty.