WASHINGTON Shortly after taking office, U.S. President Barack Obama set the goal of eventually ridding the world of nuclear weapons as a central theme of his presidency and pledged dramatic steps to lead the way.
But after lofty rhetoric and a few steps forward, Obama is facing fresh doubts about whether he is willing to take the political, diplomatic and budgetary risks that may be needed to bring his vision closer to reality.
At home, arms-control advocates who once extolled his ambitious plans are complaining about funding cuts for several key nuclear security programs, while critics on the right are leveling election-year accusations that his policies weaken America's strategic deterrence.
At the same time, Obama's efforts to spur global cooperation to prevent nuclear terrorism, which he once called the "single biggest threat" to U.S. security, have been overshadowed by the more urgent challenges of thwarting Iran's and North Korea's nuclear development.
All of this is weighing on Obama's broader nuclear agenda as he heads to Seoul next weekend for the second Nuclear Security Summit. He inaugurated the event earlier in his tenure.
"The nuclear-free vision thing has run up against facts on the ground," according to an outside expert who advises the White House on national security. "So, for now, there's going to be an abundance of talk and not much serious action."
Granted, it's been more than just talk up to this point.
Obama unveiled a revamped policy in 2010 renouncing development of new nuclear weapons and restricting use of those already in Washington's arsenal. He followed that up by signing a landmark arms reduction deal with Russia last year.
He secured specific commitments from world leaders at the inaugural 2010 summit in Washington to help keep bomb-grade material out of terrorists' hands, and independent experts say most of the pledges are being met though many were modest in scope.
But momentum has slowed on Obama's nuclear agenda and, with the November 6 presidential election looming, chances for major new advances look doubtful.
Underscoring a sense of caution, defense and national security officials have spent months debating a secret set of new options being prepared for Obama to help guide future arms-control talks. Ideas range from maintaining the status quo to reducing warheads by up to 80 percent, an official has said.
But the administration appears reluctant to push publicly on such a divisive issue as the election campaign gathers pace.
While some in Obama's liberal base are disappointed he has not done more, conservatives see his nuclear policies as a point of vulnerability that Republican candidates can exploit.
"Instead of dealing with real nuclear threats like Iran and North Korea, he's going to magic shows and talking about a world without nuclear weapons, which would be a much less safe world for the United States," said John Bolton, who was U.N. ambassador under Obama's Republican predecessor, George W. Bush. The hawkish ex-official has endorsed Mitt Romney for the Republican presidential nomination.
Meanwhile, anti-proliferation groups, which credit Obama with raising the global profile of nuclear security, are also voicing complaints. They are unhappy that the fiscal squeeze in Washington has translated into reduced spending on several nuclear security programs in his budget plan for fiscal 2013.
Ken Luongo, president of the Partnership for Global Security, a non-governmental research organization, called cuts in Obama's budget request to secure weapons of mass destruction "an assault on common sense."
Two programs at the Department of Energy's National Nuclear Security Administration were pinched hard. Funding for the Global Threat Reduction initiative, designed to secure nuclear material at civilian sites around the world, was cut by $32 million to $466 million, and will be down $500 million over the next four years compared with the levels envisaged a year ago.
A senior administration official insisted, however, that part of the drop reflected completion of an upgrade of Russian nuclear infrastructure and removal of Russian nuclear material.
A bigger hit was taken by the International Nuclear Materials Protection and Cooperation program, designed to improve security at vulnerable stockpiles of nuclear weapons in countries deemed to be of special concern. Its funding request was trimmed by $259 million in 2013 to $311 million.
Despite that, arms-control experts sees signs of progress on nuclear security efforts and caution against complacency when Obama and more than 50 other leaders meet on Monday.
Amid skepticism about the chances for meeting the Washington summit's headline pledge to safeguard all of the world's nuclear materials within four years, they are now pushing for voluntary arrangements to be turned into enforceable standards.
U.S. officials expect new commitments from several countries but are playing down the chances of any breakthroughs in Seoul. "It's (going to be) a bit of a report card and also figuring out what has to be prioritized," a senior official said.
NOT ON THE GUEST LIST
Iran and North Korea are not on the guest list or the agenda. But on the sidelines, Obama will urge world powers, particularly Russia and China, to help ratchet up pressure with sanctions and diplomacy.
But Obama is expected to keep a cautious line with countries in attendance, including Pakistan, whose ties with Washington are strained. Experts see Pakistan as the biggest area of risk because it has a large stockpile of weapons-grade material and faces internal security threats from militant groups.
Obama set expectations high in a 2009 speech in Prague, declaring it was time to seek "a world without nuclear weapons." He acknowledged it was a long-term aspiration, but his high-flown oratory helped him win the Nobel Peace Prize.
Taking that vision much farther will not be easy, even if Obama wins a second term.
With Republican opposition as strong as ever to the United States joining the global nuclear test-ban treaty, Obama for now has had to shelve his earlier promise to push for ratification.
Another arms accord with Moscow will be an even tougher sell to conservatives who say Obama he has not moved fast enough to modernize the U.S. strategic arsenal, a pledge he made in return for Republican votes that helped ratify the START treaty.
"Their commitment to it (nuclear modernization) was weak ... It turns out at the first challenge they folded," said U.S. Senator Jon Kyl, a leading Republican on nuclear issues, adding that it would be harder to trust Obama the next time.
Meantime, the ultimate test of Obama's nuclear agenda could well be what happens in coming months with Iran. Its development of nuclear arms - something it denies it seeks - could spark war with Israel and an arms race in the Middle East.
(Additional reporting by Caren Bohan, Susan Cornwell and David Alexander; Editing by Paul Simao)