The United Nations Population Fund projected last week that Russia's population will drop from 142 million today to 100 million in the next 40 to 50 years. The agency's report praised recent government efforts to increase birth rates and extend lives. But not enough is being done to counter stark demographic forces: an impending decrease in the number of women of child-bearing age, poor healthcare, rampant vehicular and industrial accidents, widespread alcoholism, and social conditions that discourage family formation.

These trends have disturbing implications, not just for Russia and its political leadership, but for the United States. No amount of windfall profits from oil and natural gas in the hands of Kremlin plutocrats can save Russia from a many-faceted decline - unless surpluses are invested in medical and social services, industrial modernization, and hefty incentives for child-bearing.

Russia's government is in denial. Officials tout a recent uptick in births. But it will be ephemeral, because it is due to a larger-than-usual cohort of women of child-bearing age who were born during a minor baby boom in the 1980s. After the Soviet Union imploded, Russia fell on hard times, and the birth rate and the population dropped. Between 1992 and 2007, there were 12 million more deaths than births.

And as the workforce shrinks, repercussions will be felt in the military, on farms, and across the economy. Ethnic Russians already worry that they will cease to be a majority in the country's far east, along the border with China. A Russia anxious about its vulnerabilities, its diminishing human capital, and its borders is likely to be a prickly partner for the West.

The need to improve US-Russian relations has barely figured in the current presidential campaign. But it should. Few other countries contain greater potential security threats. Russia still has an enormous nuclear arsenal, insufficiently secured nuclear materials, facilities that are a prime target for terrorists, and a promiscuous arms industry with clients worldwide.

On top of all this worrisome hardware, Russian political leaders harbor deep resentments over what they see as America's broken promises since the end of the Cold War. They see a high-handed attempt to humiliate Russia in Bill Clinton's expansion of NATO, President Bush's annulment of the Anti-Ballistic Missile treaty, his planned deployment of missile defense in Poland and the Czech Republic, and the recent recognition of Kosovo's independence.

Against this background, American support for pro-Western movements in Ukraine and Georgia have taken on threatening overtones for Kremlin policy makers. President Vladimir Putin and his advisers suspect that Washington has been encircling Russia and encroaching on what Russians call their near-abroad.

Paranoid or not, Russia's foreign policy elites have come to a troublesome consensus about US intentions. They complain, for instance, that the Bush administration wants Putin's help in getting Iran to suspend its enrichment of uranium, but does not respect Russian interests in return.

They fret about a Cold War mentality in Washington, an attitude that scorns Russia as a vanquished power whose security concerns need not be taken seriously. Russian strategists infer that the ultimate aim of Bush hard-liners is regime change in Russia.

The next president will have to undo the damage that was done to this crucial relationship by the last two presidents. This does not mean pretending that Putin and his handpicked successor, Dmitry Medvedev, are Jeffersonian democrats. It does mean reducing nuclear stockpiles, taking nuclear missiles off hair-trigger alert, avoiding a new arms race with Moscow, securing nuclear materials, working out mutually beneficial arrangements for natural gas pipelines, and treating Russia as a proud nation with legitimate security interests.

A Russia that is wealthy from energy resources but weak from social decline can become a dangerously resentful spoiler instead of a partner in building a peaceful world order. The next president could hardly do more for American security than to help Russia past its anxieties about the West and its own internal fragility.