There have been only two Democratic Presidents since FDR who have been elected to serve two full terms. On nuclear issues, Barack Obama seems to be following in the footsteps of Bill Clinton.

President Clinton achieved considerable success in reducing nuclear dangers during his first term, but lost momentum during his second. In his first term, Mr. Clinton midwifed the denuclearization of Ukraine, Kazakhstan and Belarus, thereby strengthening the Nonproliferation Treaty and jump-starting the implementation of two Strategic Arms Reduction treaties negotiated by his predecessor, George H.W. Bush. President Clinton expanded the ambit of Nunn-Lugar cooperative threat reductions programs in the former Soviet Union, and completed negotiations on the Chemical Weapons Convention and the Comprehensive Test Ban Treaty. Not bad for four years of hard work.

In contrast, President Clinton’s record on nuclear matters was very spotty during his second term. He successfully defused a serious crisis between India and Pakistan, and he focused briefly on ratifying the Test Ban Treaty, without success. But mostly, his attention was focused elsewhere.

President Obama also attended to nuclear issues during his first term, but significant efforts now yield smaller returns. His first term’s nuclear agenda was dominated by calendar-driven events – the expiration of verifiable strategic arms reduction arrangements with Moscow and the need for a successful Nonproliferation Treaty Review Conference – along with the initiation of summitry on nuclear security. New START was modest because the Kremlin balked at deeper cuts. The United States has now essentially joined Russia in meeting mandated reductions five years ahead of schedule. Even so, the Obama administration was obliged to endorse pricey commitments to refurbish what is now known as the nuclear enterprise.

New START’s most important accomplishment has been to reestablish a process of verifiable US-Russian reductions. Its monitoring provisions are good for ten years and can be extended for another five. A new treaty isn’t required during this timeframe, if the parties can agree to employ New START’s monitoring provisions for deeper cuts.

Mr. Obama’s speech in Berlin proposed up to one-third reductions to approximately 1,000 warheads on deployed strategic forces. While the number 1,000 is neither hard nor fast, since warheads can be uploaded on launchers if the necessity arises, the notion of a one-third reduction is nothing to sneeze at: the last time the US nuclear arsenal exceeded this number was in 1953. The number 1,000 has also been an important way-station in ambitious plans for phased nuclear reductions, and getting used to a smaller number makes deeper cuts easier to accept down the road.

Mr. Obama’s second term nuclear agenda now seems hemmed in. He doesn’t have a far-sighted, willing partner in the Kremlin. No Republican leader on Capitol Hill has championed further cuts in nuclear arsenals. Mid-sized inventories are growing in China, India and Pakistan. The Iranian and North Korean nuclear programs are stubbornly resistant to external constraints. The next NPT Review Conference could get ugly. And promises made to the Congress in conjunction with New START ratification can’t be kept with ballooning costs, questionable rationales, and budget constraints.

Under these circumstances, the White House has proposed parallel steps to maintain momentum for strategic arms reductions. In doing so, the Obama administration risks getting stiffed by the Kremlin, making the option of unilateral reductions subject to a sharper criticism on Capitol Hill.

Domestic US critics of nuclear arms reductions have the power to block treaties and brake momentum, but not to reverse course. Deeper cuts may well be mandated by budget cuts and the Pentagon’s preferences, if not by treaty provisions. The George W. Bush administration was notably disinterested in treaties, preferring instead to downsize the US nuclear arsenal as needed. Democrats may well be headed in the same direction.

Other issues have risen to the top of President Obama’s agenda – items that offer either a greater return on diplomatic investment, or hellish problems that are growing and refuse to be set aside. One example: His speech in Berlin devoted more time and a greater sense of urgency to climate change than to nuclear arms reductions. Unlike his proposed nuclear reductions, the President intends to address reductions in carbon emissions by unilateral measures and without further delay. Nuclear danger was the quintessential threat of the 20th Century. Is climate change the quintessential threat of the 21st Century? At present, killer storms figure more in the public’s consciousness than mushroom clouds.